So far they seem to be doing good. I don't think they've been out long enough for a duration factor on how long they generally run, etc.
In terms of cooling, they usually do about the best vs the heatsink/fan combos, but usually only by a few degrees. For being able to use big RAM and not need LP ram because of a big heat sink is a case for them though, removing all the heat from the center of the board probably faster than a heatsink, combo might a benefit, some have USB controls over pump speed, fan speed, coolant temp, etc, which is a cool geeky factor, and they sorta look cool.