Slow levelling has been one of the biggest problems I've had with SR as a player (I like roleplaying, but seeing my character gain power and knowing it's getting somewhere is important too) and for a long time I thought the SR system was to blame for this. But then after some different GMs I found that this doesn't have to be the case.
* Increasing the rewards, in pay but most importantly in karma rewards did a lot to give a sense of improving. (We started playing with Missions 2 and all got the feeling there just wasn't any character progression, we were gaining maybe 3-5 karma every month of playtime; at that rate just increasing a stat from 5 to 6 would take at least a year. So after some testing, we set to receiving the same amount of karma after every play session depending on how much progress we made, what/how we did etc.
* Karma for Nuyen (and vice versa) have been used successfully. (I never got the feeling this let the mage get too far away from the non-magic-users in the group. Also allowed the 0.1 essence sammy to get some better-grade 'ware because he was "stuck" and the gun nut/rigger to actually be able to one day buy that ridiculously expensive weapon/bot of his dreams (damned that ceramic components price!))
* But the most rewarding improvement in character progression ended up being roleplaying, not charbuilding, rewards. (Playing as part of a gang and saving up money to improve your neighborhood and upgrade your gang's gear from leather coats and knives to Armored Jackets with a gang logo and Predators or Uzi's, great fun! Gaining a new contact that looks like it could actually become a very valuable friend/asset if you work it right, awesome! Just being called to a meeting in a exclusive place where you get to skip the 2 hour line and just walk in the VIP entrance gave a great "look at us, we're in the big leagues now" ego boost.)