And yet another advantage of the battery grip is that you get faster frames per second with most cameras too! You would have to dig the net to find out exactly how much faster your camera gets and this is dependant on the transfer speed of your card also...
We've past the film age
Only some(and by some i mean only one) of today's camera gets better fps with a grip, I believe.
D800 for example. Not in full frame though. And the D5000 definitely doesnt have that feature.