96% of users who visit Plentyoffish are windows based 85.17% use internet explorer 11.71% use firefox. Plentyoffish is about as mainstream as you can get.
I’ve taken data collected via google analytics about how many of my users per day have vista installed and graphed it. This graph is from Feb 1st to Feb 22nd and is a sample of over 1 million user sessions per day. On feb 22nd 1.24% of all windows user sessions were vista.