I can't see how hitting the buttons, in the location on the mouse indicated in the screen shot, would either be easy or confortable to do with a thumb....
I have a mouse on my desk of a similar shape, and trying to hit even the first row of buttons using my thumb would easily cause me to loose positional control of the pointer...
If the buttons were located MUCH closer to the front, and additionally spread across both sides, this might be a feasible design.
I can't for the life of me see needing more than 8-10 buttons on a mouse however, especially in an MMO where access to f-key and number key rows and a shift/ctrl key pretty much covers it... I might like to see alt/shft/ctrl added to the mouse though, that WOULD make things easier...