I have the 4GB model so the file split doesn't matter for mine.
I tested with a new set a couple days ago. Put them in, turned it on and let it go until they died. I got right at 58 minutes before they gave out. So at least I know with regular alkalines I can fill it up. I can get a 30 pack of Rayovacs at Wal Mart for $10 so it's not bad. I've been recording bands lately that share bills and play for 30-40 minutes each so if I'm recording more than one band I can dump the files onto a laptop between sets.