Well, it used to take a lot of space for me too...Mostly because I previewed lots of stuff from dlsite and then forgot about them and let them lay there. Then, there's quality but heavy games like MGQ which was really a lot of space, and on top of that, my HD is quite small compared to what I'd want it to be (and new games taking even more space each time doesn't help at all).
Now, not so much space is taken, since I've started cleaning things up. But, giving a really rough and not at all accurate suposition, based on my forgetfulness,games I may have lying around,forgotten...Around the gigabyte,maybe. A little less, or maybe a little more.