I got the extended battery on around 12/13/10 and it does indeed run quite a long time but the phone is a huge battery hog unless I don't use it. If I don't use it, the stand by time is several days. As soon as I start using the wireless or 3G for some browsing or play something like Need For Speed, it drains very quickly.
Just charged it off the wall charger and it's topped off at 4.200V. I'll use it "normally" (for me) and see when I have to plug it back in and report back. It's 9:07 on 1/5/11. Wireless is currently off.
By the way, the phone still runs cool for me but, when I was visiting my parents over Christmas and using their Wi-Fi (802.11g) which has a very weak signal, the phone definitely heated up while using Wi-Fi. At home, it's always cool but I have a stronger signal. Apparently the phone tries to compensate for a weak signal by increasing the power to send/receive.