A recent article in eWeek said, "Enterprises last week had 11 more reasons to rethink using IIS: 10 new security holes in the Microsoft Web server and the arrival of Apache 2.0." Now that a version of Apache that was built for Windows is available, it is difficult to see why any organisation that values there website persists in using IIS.
For details see: http://www.eweek.com/article/0,3658,s=702&a=25458,00.asp