When I get home after a multi-month trip I strip the bike to the frameset, clean everything meticulously, replace chain and anything else in the drive chain that needs it, rebuild and grease lube...
Great fun and the start of preperations for the next tour. I'd never consider taking a bike to a shop for cleaning!
Its just to get all the grime and crap off, Customs in my country are a bit to jumpy, everything needs to be clean or they would take it off me or just charge me a fortune to radiate it.