Having grown up in a very dry part of the US, I think of water falling right down out of the sky is a bit weird, but I deal and ride in it anyway.

Anything from a mist to a good heavy drizzle can be enjoyable, as the rain clears the bike paths nicely, and isn't overly uncomfortable. Anything more is just no fun - but I've done it and lived to tell about it.

Actually, come to think about it, I'd rather ride in a cool rain than heat and high humidity.

My cateye Astrale 8 seems to be waterproof, but it is hidden behind my fairing, which keeps a good deal of the rain off.