Possible reasons:
1. Finder could be performing an initial index of your hard drive. This will, temporarily, increase CPU activity, thus decreasing battery life for the time being.
2. It could be because of Lion. I noticed 2-3 hr drop in battery life after I upgraded from SL to Lion. Under SL I was easily getting 7.5 hrs on basic use (brightness at 30%, keyboard backlight at minimum brightness, bluetooth off, wifi on, basic [flash-less] browsing and basic productivity); sitting on idle, the MBP was getting 10:15 on a full charge. Now, I'm barely getting 6 hrs under basic use, and 6.5 on idle. I have a 2011 core i5 model BTW.
3. As people already mentioned, things like bluetooth, keyboard backlight, display backlight intensity, and flash browsing will decrease battery life.
Also, battery calibration is only needed when you suspect your battery capacity readings to be off. If your battery capacity is currently in mid to upper 90% I wouldn't bother calibrating it.