I noticed while using ACR with CS3 in windows xp as well as ACR with CS4 in vista 64 that the program would (will) often slow down in the middle of an editting session, after several minutes of brisk performance. I've always used fast machines and lots of RAM (8 gigs currently) with these programs, so it seems to me that some kind of OS issue is at fault.
I've poked around the net a bit, and I haven't found any unifying answer to this problem. Is a "RAM leak" likely? (I've turned off as much of the vista fluff as I know how, per tweakhound.com recommendations). Is there some background service that pops up and eats up RAM? I don't know much about what most background services do, so I never shut them down on a whim. How about an ACR issue? Any suggestions appreciated.