My C230K gets about 16-17 mpg in the city, but that's 3 miles a trip between home and work with a fair amount of lights and stop signs. The car barely has time to warm up before I'm there. 20 mpg probably isn't too bad, especially with the updated EPA numbers (supposedly more realistic) being 19 and 26. Also, if you have a heavy right foot, you can really eat into the mpg, even though it's just a 2.3L 4-banger.

Pure highway mpg on my last long road trip was about 30 mpg at around 90-ish.