I've developed a problem with the gas gauge reading empty even after a fill-up. Occasionally turning the ignition key hard to the right on start-up unsticks the gas gauge.
Two other friends, one with an ML and another with a CLK 320, have had similiar problems.

has this been a common problem with this car?

Mercedes get their fuel sensors from a specific vendor. The metal in the fuel gauge sender shorts out and the gauge goes crazy. MB sent 10 engineers to diagnose the problem but as of now there is no fix. Most likely a recall?

I have seen this problem with the C-class and it was actually a mechanical problem inside of the gauge. I took out the gauge and disassebled it. I found that the paint on the end of the peg had actually sweated some sort of sticky residue that would hold down the needle on occasion. I cleaned it off and the problem was fixed!!

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM