Well, I've ran a game where someone fired a grenade into a large room with the Runner team, and even without the dodge test, no one ended up dead, even with Chunky Salsa in effect. They were using High Explosive, so the damage dropped off fairly quickly, even considering the rebounding off the wall.
I haven't yet encountered any problems in the magic+Ware department.
And as for Multiple Attacks, I've also used it in the game, exactly how it's written, and it works just fine. Decide the length of the burst you are firing, split it among the targets, Split your dice pool as per the multiple attacks action, and go with it. There's a nifty Sidebar (p.180) on the modifiers to apply to defenders if you aren't firing enough bullets at them to comprise a typical burst. Do they specifically say "When splitting bursts, you must split it this way"? nope, but it really doesn't have to, as it works just fine they way it is