Very interesting thread on Digg this morning called "Apache at 56% – what is wrong?" Apparently a number of factors are converging to erode the dominance of the Apache web server (which, as of two years ago, used to run 70% of web sites by some measures). Lots of interesting pro-IIS and .NET comments in the comments (the most vocal Unix/LAMP proponents seem to be embarrassingly out of date on the state of comparable Microsoft products — blinded, no doubt, by their rabid reaction to Microsoft businesses practices in the 1990s).
Several people pointed out that IIS today is very secure, performs well and is easier to configure (and the upcoming IIS7 adds a number of compelling features that bring it closer to feature parity with Apache). In discussions like this somebody always brings up the "free beer" argument (that Apache costs $0), but they neglect to mention that you can get the web server edition of Windows for just $300 now, and IIS/.NET is a more productive stack for developers by far. (I could easily burn more than $300 worth of time getting Apache configuration figured out.)