Yeah. Happened to me too. For some reason the update opened all your apps. Go through your apps in settings and force close every one that you aren't using. Then restart. They won't automatically start again and it'll help a bit with the battery. Good luck.
Sent from my SAMSUNG-SGH-I717 using Android Central Forums
Mine has been horrible too since the update. I flashed over GB, but then ended up doing a hard reset anyway because battery life was so bad. It didn't seem to help. Not sure what is causing the drain, but it drains by a little over 5% an hour even in standby.
I bought mine at BB like a moron ran to do the update without reading other owners comments about it and there it was, battery lasted only half of what it was with gingerbread, so I went to the store, complained and they exchanged it with a new one! so I'm still GB but battery lasts all day long,and to be honest I don't really miss any of the "ICS improvements" my phone is pretty much functional the way it is, will wait 'til good 'ol Sammy comes up with an ICS update fix