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It didn't make much of a noticeable difference either for good or ill to me. I'm sure that some people are having problems with batter life just from the amount of conversation on the subject, but I have not had that issue with my 4S. I charge my iPhone every night, and so far I have yet to exhaust the battery even with pretty heavy use throughout the day at my office (where I use WiFi almost exclusively for internet connectivity). When I'm not online for strictly work related reasons, I'm listening to music (or talking to Siri), and I get over 8 hours without a problem. Again, I'm not discounting that some new 4S users are experiencing battery issues, and I may just be lucky.
It almost looks like a coin flip as to whether someone will have battery life issues with a 4S or not. Geek.com has an article noting that they didn't experience the issue, while acknowledging that there are many reports from people who are. http://www.geek.com/articles/mobile/is-ios-5-0-1-battery-drain-20111111/