Jeff's posted two charts and a couple of tables that compare how the server products did vulnerability-wise for the 1st half of the year.
The days of risk comparison is very interesting. The total is 12 Windows Server 2003 (rounding up) and at least 900% more for RedHat overall, for high severity Windows Server 2003 had 4 days (rounding up) compared with at least 1875% more for RedHat ( 75 days RH3 ).
Jeff's inviting debate over on his blog. I'm sure there'll be many eyes over there!