I have a uni-body macbook (13").
I also have a wireless keyboard and magic mouse.
While leaving bluetooth on drastically affect my battery life?
From what I see, it's generally not too big, but is still big enough that you probably should turn it off when you don't need it.
Most of the Apple Reps say that it's no big deal, whereas all the tips for saving battery life on blogs say it kills your battery in 10 minutes. Who would've known?