I have one. I rarely use wifi or bluetooth. Or the phone itself for calls, for that matter. I charge the extended battery once every couple of weeks. It comes with two batteries. The normal one lasts several days. WiFi eats quite a bit of battery life. You can get some utilities to help reduce power consumption by basically stepping down the processing power it uses.
My friend who has one told me the new windows mobile may not support it. I have WM 5, which is pretty cool. It no longer requires you to hang up the phone while using wifi.
The Wifi is not great since it is B and not G, though. Good enough for my purposes - checking mail and sites at the airport, cafes, etc.