My experience is that in the dry their excellent. The first time when the rims were wet it gave the impression that they were worse than my conventional V brakes/pads. However, what happened next was that I panicked and squeezed the levers very hard (I've got XTR brakes) then the things locked up - deadly! So, in my opinion/experience, when the rims are wet then I need to allow enough time for the water to clear from the rims by pulling very hard in a sort of pullsating movement. Then, once clear, the only limitation is the friction between the tyre and the road. Just make sure that the bike is perfectly upright when braking otherwise you'll be going down! Normally, once the rims are cleared of water they'll remain so unless I go through a puddle or have not used them for a while.
I'm happy with them.