I would like to warn everyone who uses Skype: beware of your chat/instant messaging client if you do any kind of web development on your computer, as Skype, for some very obscure reason, uses port 80 (yes, the standard HTTP port) to connect to whatever communication server it has to talk to in order to get you online.
Fortunately, there is a way to disable this unwanted behavior. Simply navigate to Tools -> Options -> Advanced Settings -> Connection and uncheck the “Use port 80 and 443 as alternatives for incoming connections“.
While I appreciate the Skype developers’ effort to making this a configurable option, I still do not understand why on Earth they had to mess up with port 80 in the first place!
Anyway, this one was fairly easy to fix, although it did cost me some time to figure out what was happening and find a solution. There are many others that are way, way hairier to nail down.