In reply to kaotikuk:
Yes, the rock in North Wales is volcanic, so doesn't get weakened by the rain. However, you might want to think about which routes you do. Any crack climbs may have seepage running down them for quite a few days. Routes that are higher up may catch the wind better and dry off quicker. And as others have said, if things are damp, just lower your grade a bit.
One of my most memorable days of climbing was doing the Carreg Hyll-Drem traverse, which is under an overhang, on a very rainy day, when everyone else had gone to the electric mountain for the day because it was so wet. We climbed under a waterfall as the water poured off the overhang above us, and as we moved out from under the waterfall, water poured in one sleeve and out the leg of my trousers! It was a fantastic day, a stolen climb, and I will never forget it.