We’ve been getting quite a few customers asking questions regarding upgrading their 3Gs to iOS5. Here’s a couple brief notes on our findings and some places you can go for further information.

CNET Reviews Mobile section editor Kent German said that when iPhone 3G users first upgraded to iOS 4.0, manynoticed the phone slowed down and the new software drained the battery.
Apple says that the new iOS 5 software is fine for iPhone 3GS devices. The software has been out less than a week, and there are complaints from some users.The biggest issue I’ve heard from people is regarding battery life. One iPhone 3GS user vents his frustration on an Apple message board:
“Upgraded my 3GS to iOS5 on Wednesday and now it runs out of battery after about 6 hours with no use, 4 hours or less with occasional email use. Had to recharge it 3 times yesterday, and after 4 hours today…Never had these issues until this upgrade.”

If you do decide to upgrade, keep in mind that things can go wrong. And if you’re a few minor updates behind on your device, there’s more of a chance that the software will get hung up when you try to update. That’s why it’s very important that you backup up your iPhone before you begin updating the software. (To do that you simply plug in your phone to iTunes and sync it.) That way, if something goes wrong, you can completely wipe the device and start from scratch. And you’ll be able to reload it with everything you originally had on your phone.

http://news.cnet.com/8301-30686_3-20121675-266/should-iphone-3gs-owners-upgrade-to-ios-5-ask-maggie/

Everything had been going smoothly until I decided to download iOS 5.0.1. And over the past few weeks, I began to notice some of the problems that many of you wrote in to complain about.
Specifically, the sluggishness and battery life that seems to be getting worse every day.
http://www.gottabemobile.com/2011/12/12/ios-5-on-iphone-3gs-things-have-been-getting-worse/

https://discussions.apple.com/thread/3384214?start=45&tstart=0

http://www.mac-forums.com/forums/ios-apps/253358-ios5-3gs-battery-life-heat-issues.html

-Mark – Orlando iFixYouri