you have to remember that while smartphones are taking huge steps forward with advancements in a very short amount of time, battery technology isnt. our new devices have all these new features and high screen resolution with super-fast processors, but the battery that is powering them has the same capacity as my BB curve did two years ago. of course, they could come with bigger batteries, but that would make the phones even more expensive, and much heavier and bulkier. adjusting to tweaking battery settings is one of the more challenging things i dealt with when switching to android, but fortunately there are a lot of options in the OS to help.
in the settings menu, there is a battery manager that has several profiles (including a customizable one) that can essentially cut off your 3g data stream when not using your phone, which helps. you can also go into the data manager and set your social network streams to only update while you are connected to wi-fi. as a previous poster mentioned, a lot of stuff gets pushed directly to the phone. besides emails, you also get constant FB and twitter updates pushed if you are using the account setup integrated in the OS, which was the biggest culprit for me when i switched to the droid x. the battery manager will help keep that in check. there are also many people who will just download the facebook and twitter apps and use them instead, as with the apps you can request status updates on demand.
the biggest thing to realize though is that the battery life is not going to be as good as many of you are used to from BB because you now own a phone that can do more than your BB ever could. use your phone how you want to though, as there is no point to having all this awesomeness and not using it. and for me, if that means i have to get an extended battery, or carry a spare charger with me, then im willing to do it