Yea, I think everyone has their own way!
I don't race much during the week, only on the weekends. So I usually have a few days to clean the thing up pretty good. And, being winter, I don't race at all so I've been able to completely strip down the buggy (every little screw and part) and clean everything. This is quite a bit of work so I wouldn't recommend doing this all the time!
Anyways, really all you need to do for cleaning is get the big dirt off, and make sure the dirt isn't getting in the way of any moving parts. Little bits of dirt can get in hinge points and ball-ends, into the diff casing, on the shocks, etc. As long as you get those parts clean, you're okay.
It's a good idea to clean off the engine, too, because if it's caked with dirt, it won't cool off as well.
Generally, while at the track I use a compressor to clean it off after each run. When I take it home, I use a damp cloth on the parts I can get to, and then I run them over with some armor-all or those neat armor-all wipes. I never use any sort of spray liquid, nitro blast, whatever. The easy "cleaning" just makes your life harder in the long run, I think. The dirt gets pushed into places that are more difficult to reach.
I make sure all the parts move freely and clean them out where appropriate. I take off the tires and clean them up, too, but you definately don't want to dunk them in water or even get them too wet because once the foams get wet, it can ruin an otherwise good tire. A trickle of water and a brush works best for the tires, I think.
Sometimes I go a step further and really clean it, but not every time. When doing these cleanings, I'm also checking inside the diff cases for dirt and wear on the gears, as well as shocks for leaking and air bubbles.
1/8th scale has got to be one of the messier off-road vehicles; you got not only the mud and dirt from the track but you also have fuel spilling and exhaust making the dirt stick even more.