I guess if I actually kept my hand directly in line with the mouse it'd be pretty painful. I just about always keep my hand in a slant, more similar to how you'd use a trackpad, or as if you were holding a sort of slanted mouse.
I've stuck with it because of the well implemented 2d scrolling. Using a physical scrolling wheel feels off at this point.
My biggest issue with it is that it's way too heavy. Once you go back to 50-60g mice you can't go back.
That said, the change to the rechargeable version was a huge unforced error apart from the deserved mocking for the charge port location because the mouse also reports low batt condition about 10 minutes before it actually dies, I don't know what the thinking there was.
When I got an iMac I paid the $50 extra for the Magic Trackpad and it was worth it.