I very rarely do my own oil changes, I find that the setup/cleanup time, plus the material just isn't worth it. For the GM's I usually just hit up a Mr.Lube down the street, 20 minutes and I am outta there, no mess at home. Course, when I get home I always poke around and make sure everything is as I expect.
I also try to avoid touching the MB for some reason. It's not that it's overly complex or anything, I just don't have the familiarity with it that I do the others. Plus, to do the oil I'd either need a pump or remove the underside splash panel, which is a pain. For the frequency I get it done and the cost it just isn't worth the effort I guess. Now, if the car had something go wrong with it that was labor intensive/costly I'd probably break out the service manual (which I have) and tackle it....Sort of a backwards approach I guess, lol.
I have done some smaller things on the SLK over the years...belt, tensioner, rear taillight wiring fix, brake light switch, probably some other stuff I can't remember.