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Apple says 7 hours, but I would guess 4-5 of actual internet usage. Flash, closer to 3.5-4.
 
OSX leopard partition for textsurfing, notes, ichat, itunes
8:00-8:30 on half to almost full brightness.

OSX flash and movie watching
4:30-5:30 depending on brightness

XP SP3 bootcamp for textsurfing and youtubing/flash
3:00-3:30

XP SP3 VLC movie watching
2:30

Unibody MBP 15'' 2009 2.66ghz 320gig hdd.
If you don't use flash on osx, and go surf on say macrumors or engadget while word processing and such, you can easily pull 8:30. I know. I do it every weekday to pull off my classes =]. I thought the builtin was 8hrs advertised. Oh well, everytime I pull out the charger in the morning and am about to go to school, I check to see the battery always above 8+ hours =].
 
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