2.0 vs NXT for reliability

None that I know of with the hardware. There *has* been a glitch in the software, in that some users (I wish I knew what fraction) have had their NXT bricks enter "Clicking Brick Syndrome", a state where the NXT just sits there and clicks, waiting for a firmware update. It's actually suppossed to do this, but some small percentage of the new users have had their NXTs lock up completely when they tried to update the firmware. This is, (as near as anyone in LEGO or NU can tell me) and software issue at this point, and one with a potential fix already being tested.
Yes - the NXT has no IR ability, which makes wireless communication with the RCX a problem. The NXT is also slightly bigger, and more power-hungry (although not a whole lot, when you consider the stength of the motors in particular - they are much higher torque). Right now, the RCX has more programming options (RIS code, Robolab, Forth, Java, NQC, BrickOS, etc.), but then again, the RCX has been around for a looong time, while the general public has only had it for a couple of weeks. The MDP has already made strides on third-party software, and has already built and tested third-party hardware (compass, multiplexers, IR bridge to the RCX, and others).
It's a nice toy. The RCX is still wonderful, and I'm not giving up mine anytime soon (like, anytime at all). But the NXT has a lot to recommend it. I'm really liking BlueTooth and the "free" (as in built-in) motor encoders, and the software to take advantage of them. Very very nice. OK, and they are a lot of fun to make Zamor-sphere launching carnage with as well :-)