Just finished my 220 and if I were to build another it would certainly be a little lower (20 vs 32) I'm having a heck of a time getting to the bottom of the tank and lighting is much more expensive.
Just my .02 (and probably worth even less),
Paul
I just got a 120 for christmas and the dimesions are 48x24x24. To me this is perfect for a reef tank. It is deep from front to back so you can create different levels of reef and it looks more natural.