I don't find it to be 'clumsy' at all. I find it to be amazing and feel like a dream in my hands. I am not just fanboy trolling, I really love holding it.
My only complaint on the 'feel' of it would be accidentally hitting the back touch bad when im trying to get into a deep gaming session!
It feels ok to me, but it will feel pretty weird to me if I play my vita right after playing my ps3 or 360, because everything is so small.
I would really like the next version to have slightly larger buttons maybe, or at least make them less plasticy and clicky and make the L/R buttons less loose feeling. Id like the D pad and buttons to feel like the Dual Shock and PSP buttons and not be all clicky when you press them, but its not that bad once you get used to it.
The vita does cause my hands to become uncomfortrable after a while but that is normal I think for a 25 year old using a handheld anything.