I'm not a huge fan of Sub-D and I recently had to do a hand for class as well. If you have to use Sub-D or really have your heart set on it thats fine though. However, I'd start with a poly cage that stands pretty well with the general shape of the hand first and then convert it and crease the tendons and all that.
I second the comment Jay made about the thumb. I'm certainly no expert in any of this, but my usual estimation for the thumb is ~ 30º around the forearm axis and ~10º down from the index finger. I think that'll help it from lookings so flat. Look at your own palm for how the connection really occurs... once again I think its easier to visualize in polys at that point, but that's just me.
In any case, this one looks good - but I bet you could do better. good luck.
[edit: oops just saw that you were doing polys now
find some nice references and you should be good to go]