I have recently noticed that the battery meter on my MacBook shows approximately 50% less time remaining on battery when I am signed into my Facebook account than when I am not. The fan noise increases as well.
By default, Adium signs onto all accounts when I start my machine. I have noticed that even though it was charging overnight (the MacBook is a month old), the battery would show less than an hour left shortly after startup.
The Adium icon on the doc showed the duck with a spinning black box to the top right. I closed Adium and the time returned to an acceptable 3+ hours. I then restarted Adium and noticed the previous drop-off. I signed off of all accounts, then signed back on one at a time, noticing that only Facebook causes the meter to read incorrectly.