I've been playing crysis 2 since release and I always had some kind of problem with crossfire&flickering etc.
First of all, my rig:
-Processor: i7 730@3.3ghz with turboboost on
-Video card: ati 5970
-Vcard drivers: catalyst 11.5 hotfix b + profiles 11.5 cap 3
-RAM: 6gb@1333mhz
-OS: Windows 7 64bit
Now I've always found a way around all the problems by myself or reading on forums, but rarely got an optimized performance: for instance, I usually don't have 60fps in multiplayer, but a few months ago I managed to get there (i think it was patch 1.2).
The real problem is that every time new graphic drivers, profiles and a new patch of the game comes out new problems appear.
Patch 1.8 introduced advanced graphic options, which gave us a few more choices (but still not as many as everybody wanted). It also brought to many of us new, horrible graphic effects. Cryadam announced it was due to disabling motion blur, but I didn't find this to be the case: infact, I can disable motion blur without any problem. My problem appears to be post-processing or, better, the console command: sys_spec_postprocessing. Here's a short video showing the problem: