I apologize for the issue. I’ve not heard about major issues after 5.1.1 update. In fact, couple of enhancements/fixes was done on 5.1.1
• Improves reliability of using HDR option for photos taken using the Lock Screen shortcut
• Fixes bugs that affected Airplay video playback in some circumstances
• Improved reliability for syncing Safari bookmarks and Reading List
• Fixes an issue where ‘Unable to purchase’ alert could be displayed after successful purchase.
I would suggest you to turn off wifi and update your device profile(Tap Key Pad.Type ##UPDATE# (##873283#). Phone will process updates.Tap OK.When Service Update is complete, tap OK. Phone will display searching in upper left corner.When Sprint 3G is displayed in upper left corner the update is complete and you can use your phone). Let me know.
No problem here. As I recall, the install took a while and you needed to wait around for the phone to do a few things.
The only change I noticed was a difference in how the phone represented a battery discharge (seemed to stay on 100% while discharging for a while, but didn't last any longer).
Check if the update was installed:
Settings > General > Software Update > iOS 5.1.1 Your software is up to date
Try restarting your device (see image for instructions), If that doesn't work, try resetting your device (last resort):