I'm running a Zelman 9500 on my E6700, An it's really not "that" heavy", At least not enough to hurt the mother board by any mean's.
I read review's that install was hard to do an people ended up cutting themself on it alot trying to.
I must say I had no problem at all an took me about maybe 10 minute's at the most, An that's with applying my AS5 to the cpu.
It really is big no doubt, Much bigger then I thought it would be. But to tell you the truth, I believe one would have no problem putting it in a mid sized tower. Aslong as your CPU slot is far enough away from your GPU.
Here is a photo I took when I got it installed on my board.
< I wasn't done building yet but seem's to be the best one I can find of a good shot.
I've only got my E6700 clocked up to 3.06 so far.