The Black Ops launch has been less than smooth for Activision, particuarly in regards to the PC version. You can read more about that here.
Treyarch has recognised the problems, and issued a response to gamers who opened support tickets in relation to the problems.
Hello,
This is in response to your ticket regarding Lag. We are in the process of rolling out an update to the black ops server configuration. This will be automatic. After testing, we have found that our update will significantly improve performance on all servers.
No action is required to be taken by you. Please, we appreciate your patience. This roll out will happen in the next 2-4 hours. Please wait 24 hours before submitting any additional support requests regarding lag, as your issue will likely be resolved as a result of this change.
Thank you,
With any luck, the patch will be live in the next few days and the game will be in good working order.