What are the project GUIDs in a Visual Studio solution file used for?

Question

I have multiple projects in a single Visual Studio (2008) solution.
I just discovered that each of these projects uses a same GUID, so in the solution file it looks like

Answer 1

Project persistence block in a solution file has the following format:

Project("{project type GUID}") = "", "", 
    "{}"
EndProject

So it's expected that first GUID is non-unique, it uniquely identifies Visual Studio package that handles this type of projects.

The GUID you posted is interesting - it looks like mangled C# project GUID, which is FAE04EC0-301F-11D3-BF4B-00C04F79EFBC. Did you change it yourself or is it a posting issue (e.g. you are using right-to-left locale such as Hebrew or Arabic).