I had V 10.0 put in my ML when it was serviced back in Feburary, it was offered as a free update to a Feb 2008 car.
I think that it is actually quite good as it does not tell me I'm 'Off Road' at every recently completed bit of new road the way my 2007 S Class hard drive version does.
My opinion may by clouded by the fact that it was a freebie and that I have something older to constantly compare it to.

I like the on-screen ETA which takes about 5 mouse strokes to get up in the S!
It does seem to take a little longer to learn the best routes compared to the hard drive!