Skype listening on http / https by "default".

Your webserver isn't starting because ports 80 / 443 are in use? Well, it just might be... Skype. For some reason, it listens on ports 80 and 443.

telnet localhost 80
GET / HTTP/1.1
HTTP/1.0 404 Not Found#

Yep, we have a webserver listening allright. Let's find out what process it maps to.

netstat -ban

Active Connections

Proto Local Address Foreign Address State PID
TCP 0.0.0.0:80 0.0.0.0:0 LISTENING 324
[Skype.exe]

TCP 0.0.0.0:443 0.0.0.0:0 LISTENING 324
[Skype.exe]

As sure as hell, there it is. (use lsof / netstat on UNIX systems to match an open port to a process).

Skype listens on these ports by default and acts as a call/message relay, and you can close them by going to Tools - Options - Connection - Unticking "Use Port 80 and 443".

More info on being a Skype "supernode" or relay node is available on the Skype Forums.