I have been using it for a while. But having said that I only know about the bits of the program I need to do my designs. I ignore the rest which is probably over 60% of its capabilities. The other thing is is OK to just play withe the program. Hit "Ctrl+z" at any time and it undoes what you have just done (if you make a mistake).
Glass Painting yea. I used to use GIMP a lot when I got my first graphic tablet (a slate 2 in one). Now I don’t rly use it anymore cuz the program brushes have a lot of pixels. And I have a new graphic tablet.