The current resolution depends on your desktop resolution. I keep it in Windows Mode because I don't need to throw away all the video memory allocations, allowing you to bounce from map editor to test game very quickly. If we went Full Screen Mode during test game, I would have to re-load all the textures and geometry (or worse, store them in system memory and recover the data that way). If there is interest, I might experiment with a mode which DOES load in the assets again so you CAN bounce from an IDE at 1360x768 and run test game at 800x600, but it's usually easier and more convenient to change your host resolution as the reasons for wanting the test game to be 800x600 are the same reasons to have the map editor also run at that resolution as they both suffer from the same performance penalties during rendering.
Hogging the awesome since 1999