While the single player I found to be fairly consistent in terms of framerate (If less than ideal), multi player is where the framerate problems having a more significant impact on gameplay.
System Specs:
Q9550s @ 3.2Ghz
4GB DDR2 900Mhz
HD6870 @ GPU-1000Mhz RAM-1050Mhz
Currently I can run CODMW2 at 1920x1080, 4xAA, 16xAF, Max details at a minimum of 75fps after a several hour long play session in multi player.
CODBO on other hand struggles at 1920x1080, No AA, No AF, max details at a minimum of around 30fps after a several hour play session.
The most unfortunate thing is the inconsistency, which really hampers competitive multi player. Black Ops will range from as low as 30fps on a long view of a level firing off some rounds into smoke, where other sections of the game run out at 100fps in a less visually intense setting. However the drop in framerate does not seem consistent with the drop in visual presentation on screen. i.e. 30% more visual information on screen results in framerate dropping by about 70%.
Even moving details down to low settings doesn't seem to aid the minimum framerate much if at all.
Definitely feels as though the game is not leveraging all of the processing power there and given its visual similarity with MW2, it seems unreasonable.
Moving away from this the server browser is unresponse and slow, hit registration and general netcoding is lackluster to say the least (most evident when watching a kill cam).
TIP: If your game requires as many or more manual netcoding tweaks to the game configuration file than decade old copy of Counter Strike, maybe you should try again.
I am using a very new video card (the HD6870) so I anticipate having a few more issues than some pending driver updates, however it is still very disappointing that a game of this caliber launched like a copy of Stalker. This is made more surprising given that all indications (Dedicated servers, promise of COD Tools) suggest a reasonably savvy PC development team pushing for all of the MP PC fundamentals removed from MW2, only to have the game fall flat simply because it wont run well on decent hardware.
All issues aside I feel it's worth commenting that the overall product does feel less polished than previous Infinity Ward installments. However that does not necessarily imply that this is not a finished product and much like WAW it gets all of the fundamentals more or less correct with a few new features. The only problem is that if you are going to buy an IP and create what is essentially the same product, with extras, you are inherently going to be compared directly to the previous installment, for better or worse.