I have had a Cateye V3 for a little while now and it's really a nice bit of kit. And I can confirm after the very wet weekend we just had here in England, it IS waterproof!!
I have an annoying problem with it though: sometimes when I stop during a ride for a little while (not a red light type of stop, more like a "café" or "puncture" stop, i.e. 10-15min), the V3 seems to lose the connection to the transmitter. When restarting, the speed and cadence are stuck at 0/0 (the HRM works fine though). I have to go to the setup menu (using the button at the back) and re-pair the speed sensor, the speed then comes back.