After discovering that the Tweetie app I use turns on the discrete GPU, I've been looking at alternatives to maximize battery life. A lot of twitter clients use Adobe Air, which also seems to get a bad rep, but is that because it drains battery life too, or because it's just buggy otherwise? So far I've been using twhirl without any obvious issues, and I'm testing out the battery usage with that running. I have to admit, I didn't notice any significant battery drain when Tweetie was running, so maybe I'm just overreacting here. If I remember right I got a little over 6 hours, and installed Tweetie about two hours after I turned my MacBook on then. I'd actually prefer twhirl since I use that on the desktop and I'm just used to it, but not if Adobe Air is going to cause problems on my shiny new MacBook. 
