I've got all of my projects spread out over a number of computers, and in different directories, so it's a bit hard to give an exact number. But it's definitely 1GB, at the very least.
I guess alot of it is how many backup versions of a project you save; I have 50 copies of gridquest in a folder on my harddrive, and a whole ton of copies of its loadable data scattered around. Actually most of my stuff is scattered- that TGF only contains the stuff I've worked on in the last year >.>
Aye theres about 20 or so various backups in there, a couple of other projects and an external library of sound, music and video files. Surprised it's only 3gb to be honest.