For rec riding I'd skip it if it was raining. If there's a high probability of rain I might skip it too, but if I went out I'd take a bike with fenders, and the route would be a more circuitous one where I can b-line it home if it got bad.
For commuting, I'll go out regardless of rain. Seems like this spring has been particularly bad for rain. I feel like I've ridden in more rain this year than any other.