Yesterday, during my 13hours *cough* testing session, I had the following happen once to me:
Everything was running smooth, I was flying over V2 when suddenly I heard multiple explosions and I went from 39fps to 5fps. I figured this was due to a bomber having carpet bombed the V Base.
I tried flying away from the area, thinking FPS would get back to normal when I got out of the smoke/bombed zone. I flew as far as A22 but FPS was still at 5. I had to exit AH & reboot to get it back to run smoothly.
This happened only once so far.
http://www.onpoi.net/ah/DxDiag.rar