I use a hose all the time as well to knock off the dirt wherever I can get it. I try to not spray into stuff, but I'm not overly cautious. After it dries I oil the chain.

Every 2 or 3 weeks I'll do a thorough clean job with a bucket of water, a rag, a brush and the chain cleaner (that citrus cleaner stuff works great on the chain).

I would advise against using a power spray at a carwash, I've seen people doing that. Its got to push water into the bearings etc.

John