I srtated getting some serious slowdown on my machine this evening whilst watching a replay. I checked Taskman and I was running at 33% load!
My specs are i7-3930K, socket 2011 mobo, 32gb ram, 2 128gb ssd's 3 sata drives of 2tb or 1tb size, ati gigabyte 7970 GFX.
Picture says it all, but basically I had about 4 FAforever processes running the background each sucking up about 8% load, and practically maxxing out the second core (which is just unheard of on this machine except when transcoding large files in HD). Looks like a memory leak to me.