Playing with a band does SOOOOO much for you. I played for nearly 2 years as a "bedroom guitarist" before joining a band. Then I joined an informal band (we didn't really gig, but we jammed a lot) and I pretty much quit practicing at home. I would only play with the band. My girlfriend of about 1 and 1/2 years then is brutally honest when it comes to my guitar playing (you need someone like that though, to keep your ego beaten down), and she says my guitar playing got better in the 6 months with the band than in the year before that. I thoroughly believe that a 20 minute jam session can spawn more creative ideas than an hour of practice alone.

Being up on stage is so different from anything else. The first time I got up on stage was with my church band, me playing improvised lead guitar. Looking out to 200+ faces will quickly make you think twice about just playing whatever, and you're forced to think about what you're playing. I've played many songs in which I wasn't thinking - letting my fingers dictate the music - and being up on stage totally changes that. The adrenaline pulsing through your veins gets you on some kind of weird high and you really get into the music. RECORD WHAT YOU PLAY THEN! It will either be the best (if you get into the music) or the worst (if you let stage-fright/tension take over) that you'll ever play.