Ya its kind of suprising. I actually don't have any bugs running MIUI. The Camera button doesn't work(I didn't realize how much I used it), but other than that, it hasn't been buggy at all for me. I SBF'd, went to CM7 and then installed MIUI. I wonder if people that have a buggy install are coming straight from .340. I've never had any issues at all. One of the most complete roms I've ever used.
As far as battery life, I've run Apex, Darkslide, Liberty, SS, Rubix and CM7. I'd have to say in order as far as Battery life, Apex, Liberty, Rubix, SS, DSX, MIUI and then CM7. Apex, Liberty and Rubix were significantly better. I have had others roms also, but battery life was premium with those. Personally, I prefer MIUI over all other Roms. The configuration ability and just the clean bugfree way it works for me is absolute perfection. I'm running MIUI 1.8.5 which does seem to be a little worse than the previous 1.8.2... Hope this helps..