Since the Steam forums are down I'm looking for help with a problem that popped up just today. I was innocently mapping away, placing an areaportal in a doorway, and suddenly when I tried to move in the 3D view the camera had gone all jumpy and the view only updated about once a second. Using everything else is absolutely fine. I don't think it's to do with the amount that's on-screen because I opened up a larger, complete map to check against my smaller, incomplete one and the performance drop was actually less noticeable on the larger map. Here's a video to better demonstrate what's going on: http://www.youtube.com/watch?v=CbOWLDtkdBM I've tried refreshing the Source SDK content and nothing has changed. Even if I switch the 3D view to flat, untextured mode there is zero performance increase. The FPS rate is so bad that I physically can't move around my map accurately enough to continue working on it. Other games like TF2 work fine with no performance difference so I don't think it's my graphics card, especially as free look without moving is smooth.