Switching off automatic time-zone sensing in iOS 5 can improve iPhone battery life significantly, according to iDownloadBlog. The site claims that a bug in iOS 5's GM release causes the GPS-enabled location tracking connected to the automated time-zone function to run constantly. This unnecessary use of the GPS circuitry may drain the battery exceptionally quickly.
To fix the alleged bug and avoid the battery drain, head to the Settings app in iOS 5 and tap Location Services and then scroll to "System Services" at the bottom of that window. Then switch off "Setting Time Zone".
It's not an official bug yet, though Apple is reportedly working on iOS 5's battery life issues. Anecdotal evidence suggests flipping this switch may significantly improve battery life.