[Rockopolis]

I've been designing a mentat character, and I'd like to play one, but I'm a little dry on things to do with them, or things I can do with them.
I think with Exceptional Attribute, Genetic Optimization, maxed Cerebral Booster, and a hit of Psyche, I can hit 12 Logic; plus all of the Logic linked skill Augmentations, like Qualia or an Encephalon.
But I don't think I even understand what 12 Logic means, let alone what I'd do with it.

EDIT: If I understand the rules correctly, and you can use Logic in place of the Hacking (the chart indicated it was defaultable) skill (with the one point penalty for defaulting, then it is to your advantage to not know Hacking.  "I cherish my lack of preconceived notions.".
Though I'll have to check which dice pool Augmentations apply to what.

[Xzylvador]

... I can't really imagine that kind of intelligence, but probably the guy would be smart enough to become a bazillionaire without having to risk his life running the shadows, despite any drawbacks he might suffer.

[Makki]

EDIT: If I understand the rules correctly, and you can use Logic in place of the Hacking (the chart indicated it was defaultable) skill (with the one point penalty for defaulting, then it is to your advantage to not know Hacking.  "I cherish my lack of preconceived notions.".
Though I'll have to check which dice pool Augmentations apply to what.

not really. you would default on Program rating minus one. There is however an optional rule to use Hacking+logic instead of Hacking+program

I have a high logic built here. An Adept gunslinger/medic

otherwise, what Xzylvador said

[Valashar]

Should note that intelligence doesn't automatically equate to education or knowledge (although, yes, you do get massive points for knowledge skills), so there are plenty of circumstances in which our intrepid 12 INT character would be a runner.

That being said... some entertainment examples of what such a character might be able to accomplish:

The Pretender (someone who is capable of not just talking the talk when talking on an infiltration role, but walking the walk as well with only a minimal time for familiarization)
MacGuyver, or rather the guy he wants to be when he grows up (consider the kind of improvisational skills someone with that mental capacity could have... who needs to bring gear, just use what's on-site)
Nathan Ford of Leverage (this is the guy with The Plan... knows the full plan, all contingencies all the way down the regular and cyryllic alphabets (in the pilot ep, he gets down to plan J on their first job alone) and knows them for everyone on the team)
Nathan Stark of Eureka (the guy created a fully sentient AI housed in a body that passed perfectly for human by accident, and was more than functionally familiar with every single project and experiment in the place... and when he didn't know, it didnt' take him a lot of time to catch up... this is the kind of guy Xzylvador is talking about as far as not needing to be a runner, but I kinda think he'd still want to be, just for the fun of it)

[Makki]

MacGuyver, or rather the guy he wants to be when he grows up (consider the kind of improvisational skills someone with that mental capacity could have... who needs to bring gear, just use what's on-site)

just get Jurryrigger and every technical skill at one, so you don't need to default (some you can't). remember, skill 1 means "has done it at least once before".  Your guy could have a cool attitude of "well, I have seen helicopter before..I'm sure I can fix that one , too..."

[Canticle]

Someone with a logic 12 is definitely trans-sane. When you have an amateur knowledge of a subject like Quantum Physics, if anyone speaks to you about it intelligently without simplifying the concepts you don't understand. Now, someone with logic 12 would be babbling about the sentience of AI and their rate of cognition while ignoring syntax and using words from any language they knew that best described what they were trying to say.
People think he is crazy and no one can understand him without someone who synthesizes the information that the logic 12 is spouting out with a sort of Chinese Room scenario.
The logic 12 character would be a great runner who is a planner or hacker, but there would have to be someway for the other characters to understand him.
Peter Watts's Blindsight handles this problem.

[Kot]

Blindsight is a great example - the way the main character handles detachment from the human race because of his cognitive abilities is the best part of the book. And the character would be having problems with everyday life and people being stupid... Thus, it's a really good idea for a reality-impaired character...

[CanRay]

Go so completely batdrek crazy that Nikola Tesla will invent a time machine just so that he can go, "Hey, you're giving a bad name to scientists!  Try acting more like a normal human being!"

It might take him a week to develop and build. 

[Rockopolis]

I'm liking the ideas, and yeah, whether attribute progression is linear or exponential, I can't imagine that amount of intelligence.  I mean, when they're strong or fast, that's easy, but when they're smarter than you could hope to be.
Someone with that much Logic isn't really a playable character?  Or at least it seems to move into houserules and 'use your judgement' territory.

Blindsight and the Chinese Room, I'll have to look into those.

Although I think the optional rule is to limit the Logic+Hacking rule to the program limit, I like the idea that they're doing it without a program.  "What?  Of course emulating technomancy is impossible, for you.  Ba-zinga!"

I think it's funny, although I need to add Cereberal Boosters and recalculate when I get to my computer, that Im using standard ware and still have three and change essence left.

Motivation is a bit of a problem; this seems more like the person to hire (or manipulate) Shadowrunners if they have something they want done.  I can only really think of arrogance or strained circumstances to see them doing it themselves.
More jokingly, they're doing it because Shadowrunners gain karma faster than anyone but Prime Runners.

[Rockopolis]

Hmm...I suppose, if nothing else, you could make money renting out comp time on your brain.

[Glyph]

Remember that mental ability is split into four Attributes.  A high logic means you have superior analytical, mechanical, and information processing skills.  But charisma is used for manipulating or mentally dominating people; intuition is used for observation, picking up clues, and acting on instinct; and willpower is used for resolve, determination, and the gumption to get things done.

Someone with high Logic, but average or lower in other mental attributes, would be gifted, but not mentally superior in every way.  A high logic character would shine at quickly understanding complex concepts, and anything to do with fiddling with or fixing things - biotech, explosives, chemicals, and so on.  You are best off getting a smattering of a lot of skills, because many logic skills can not be defaulted on.

[Fortinbras]

Makkie touched on this, but I would like to emphasis that you can't default to Logic while hacking. FAQs clears that up.

Computers are just running too fast for the brain, even a brain with a Logic of 12.

[CanRay]

"Well, after I solved the minor problems of the UCAS debt and the easy solution to the HMHVV..." 

[Longshot23]

"Here I am, brain the size of a planet, and they tell me to [insert menial task here] . . . call that job satisfaction, cos I don't . . ."

[Rockopolis]

Well, I've heard about a Mind Over Matter Adept power several times...
With 12 logic, you could probably analyze thousands of recorded firefights to determine the statistically most advantageous positions and actions.