I'm creating a game and use GLEED 2D as level editor. It works really great!
I have some small improvements that would make it easer to work with the editor:
1. Possibility to pass a file name argument to the GLEED 2D executable so you can select "Open with..." on a XML file in Visual Studio".
2. Option to make the ContentRootFolder relative to the location of the XML file. This way you don't get errors when you move the project or when you use version control.