This is why I always wait to buy my latest gadgets, even from Apple:
Today, my iPhone died after about 8 hours–not even enough to get me through a full day without recharging (and this is typical). This was not 8 hours of constant use (unless you count the constant pinging of notifications, which may be the culprit). It was 8 hours total from the time I unplugged it in the morning and took it with me until the screen went black at around 4 PM. According to the specs, the iPhone 4S is supposed to get 200 hours of standby time, 8 hours of talk time, and “up to 6 hours” of Internet use on 3g. During the day, I made half a dozen calls less than 5 minutes each, used the Internet for an hour on the train (email, Twitter, light Web browsing), and then maybe another 90 minutes throughout the day.
My rule of thumb when upgrading operating systems for my desktop Mac and my iPhone and when buying new hardware is to just wait. There’s no correct number, but most of the time this means waiting 3-6 months.
Usually in that timeframe bugs have been fixed software patches have been released.
Most of my non-techie friends automatically assume I’m first to get any new Apple product. While I’m aware of the latest developments in the tech industry on a daily basis, I wouldn’t call myself bleeding edge when it comes to purchasing gadgets.