Sorry, haven't read the whole thread where this may already have been mentionned - the poll title is grip or no grip but no grip isn't an option in the poll!
For me, no grip.
As Yvonne will testify, I'm another shovel hander but manage to use a selection of Nikon bodies from the small (F65 [not often used these days]) whick looks like a compact in my paws to the just perfectly sized D700 via an F80 and a D70. Tried grips on the F80 and D700 (although not for very long) and couldn't get along with the balance. I'm more than happy to confess that it was more a play with the grips to see how they felt than a proper test drive but that brief experience was enough to give me the equivalent of car sickness.
The only possible benefit I can see in the things is to give you another shutter release to avoid that oh so onerous task of turning the wrist through 90° (which, again, I'm more than happy to admit may get tiring after 90 minutes shooting a soccer match in portrait orientation).
I should point out that the vast majority of my photography is in 3:2 rather than 2:3 so I have very little practical use for a grip anyway and that I'm a Nikon user. Then again, the reason I shoot Nikon is that I chose the first Slr on (to a large extent) ergonomic grounds after test driving several brands (including Canon, Pentax and Minolta) at the same price/spec point - maybe (NO inflamatory intent) Nikon are just better handling?!
OK, you also get the extra battery (which I know on the D700 gives a few extra frames per second - but I shoot stills not a machine gun) but be honest, a good battery will give close to 1000 shots and that should be plenty for 45 minutes (a half) of reasonably hectic action at which point you can simply open the battery door and swap the tired one for a fresh one. I can only assume that you're shooting hand held, so the extra weight will be tiring both while shooting and transporting. Not sure whether my D700 will even fit my kit bag with a grip fitted either!
They DO make the camera look more professional though, don't they?