Netcraft.com gives the following details for meta.stackoverflow.com SO is an ASP.NET app so IIS should be the server, since MONO isn't full featured yet.Given that the details for meta.stackoverflow.com match pretty well.
The Netcraft data for stackoverflow.com stackoverflow.com however shows that it runs on Linux with a history of Linux + IIS. (Now www.stackoverflow.com also shows that it runs on Linux, but since it primarily does a 301 to stackoverflow.com, it could run on anything.) Data for stackexchange.com also shows that it runs on a nginx server on an Unknown OS. While previous history of Win Server 2008 with IIS 7.5 exists.
Now these signatures, I hear, can be easily spoofed(they can also be misleading), but are they and if not can the-powers-that-be give us some insight.
Update: There is also the minor issue of netblock ownership. The records differ for SO & SE, but that is off topic for this question.
Update 2 And we recently were told that meta.SO is moving to NYC, the IP as per ip2location says the IP 18.104.22.168 belongs to CHICAGO