I played some multiplayer Call of Duty: Black Ops
on the PC yesterday as part of my review process and I did experience some performance issues even though I have a pretty beefy machine. It looks like a patch has come out
to address some of those issues. I haven't had the time to try it out yet, but I hope it does take care of it. The issue does crop up in single player as well but it doesn't seem the release notes address that. Perhaps the fix to multiplayer performance applies to single player as well.
Updates to Call of Duty: Black Ops - Multiplayer have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:
Call of Duty: Black Ops - Multiplayer
* Friends fix for join in progress and Friends tab in server browser
* Performance improvement for dual and quad core systems