in terms of being upright on the back wheel i find this has a lot to do with the wheelbase of the frame you ride. For example i used to ride one of the old skool giant frames (the yellow ones) and i found that my weight was pitched far back of the end of the bike, with my front whell was still quite low. After having a couple of frames i now have a lenghty bt frame which enables me to be much more upright on the back wheel, and makes manuvering on the back wheel a shit load easier. chainstay lengths obviously play a part, but i think the reach is the main factor.
basically, when on the back wheel...
short reach = lower front end, harder to manuvre on the back wheel
long reach = higher front end, more steep on back wheel, generally easier to manuvre (easier to boon)
this is just from my expirience.
Rob