I wash mine religiously on a Sunday afternoon, unless it's raining, in which case I just spray it with a hose to get the muck off. If I have time during the week I'll do it too, I do my wheels about 4 times a week if I can, again, depending on the lovely Irish weather.
I also know a very good valet place based in one of the carparks I use for work, if he's not busy and he sees me coming in (and I make sure he does) he does a great job and doesn't charge me

But, I can't do that too often or it's like I'm taking advantage.