I figured since there are alot of car guys on here that I would post this.
Recent Department of Transportation data for complaints they received per 100,000 cars sold from 2001 to February 3, 2010 (reported in Newsweek)
So, to clarify this data, VW owners complained at an approximate 10 times higher rate than did MB owners. Different sales volumes are not relevant, as this rate is based on per 100,000 cars sold. This is not warranty nor repair data, but complaints to the DOT, and all sorts of variables may be involved (e.g. propensity to complain to the government, for example)