My first day with the extended battery showed these results:
I had charged it previously and let it sit a few days. When I installed it, it showed 93%. I was using the Hotspot feature most of the morning so I had it plugged in. I unplugged it at 11:30 am. It showed 100% for the first 2 1/2 hours of use. Phone calls, texting, facebook, (1) foursquare check-in, Stupid Zombies, Sudoku, internet.... I rebooted to see if the battery percentage would reset and it did down to 89%. Not too bad. I continued to use the phone normally as I do everyday as listed above. I'm pretty much on it about 75% of the time. After 9 hours of use the battery had dropped down to only 53%.
I can deal with the added hump for this kind of performance. I just wish someone would release a decent case for it.
On another note. I used the standard battery yesterday while traveling out of town for an interview. With the phone off most of the day for plane travel and while onsite for four hours for the interview I was at 16% before I left the airport for the trip home. Ridiculous......