Particle effects performance.

[Flanker15]

I noticed that Cod has that all too common problem of heavy framerate loss when too many soft particle effects (mainly the nice dx10 smoke) get close to the camera.
Not to bad in other games but in a game where you're often flying through your tracer trails or behind a burning plane it can be problematic.
Might improve with the multicore patch but still something that could be better optimised.
Other places you'll notice fps drops are the dust that comes off a sliding plane and when you crash (the water/smoke effect).

On the flip side: Particle effects like smoke don't have any long range LoD, so when a burning plane gets beyond 1 km from the camera it just stops spawning particles. Smoke (mainly the big smoke) and other trails should be visible out to the horizon in some form.