I don't mind walking in a light drizzle if my walkman and earphones aren't in danger of getting too damp. Or if I'm hiking. I just can't "power walk" while wearing a bunch of water resistant clothing and shoes. Hiking though, I don't mind doing it in the rain. Especially if I have a warm, dry change of clothes to dress into right after. With a cup of hot cocoa or tea. Mmmm... 
