I think Pantheon sucks the juice out of the Galaxy. I am running 2.1 on mine, but mine came ready shipped with it from 3, and in my opinion, the Galaxy seems to be more efficient than other android handsets. My girlfriends TM Pulse drops power like a brick dropped from 20 stories up, so I figure you have something installed that is doing the battery drain.
Change the Home app to something lighter like ADW_Launcher. Also turn off any services you don't need, when you don't need them, like GPS, Bluetooth, WiFi, install a good task killer, and set it up to autokill. Some seemingly innocuous apps just murder the battery, for instance, I normally get to the end of a whole day with around 80% battery left, with GPS always on, and I use the camera a lot, but if I leave instant messaging apps on in the background, and it can be 30% left or less by end of the day.