The Team Foundation Server 11 beta is available for download, including a "go live" license and support, meaning that you can start using the beta for real projects and there will be a supported upgrade path to the final release. If you are using an earlier version of Team Foundation Server, then you may want to consider upgrading to the beta.
Most scenarios will "just work" when upgrading to the new release. However, depending on the complexity of your existing Team Foundation Server deployment, the capabilities you are using, and the customizations you have made, there may be additional steps for you to consider in order to ensure the smoothest upgrade path.
To help you in this process, I just uploaded two Channel 9 videos by Ed Holloway and Ewald Hofman who are both on the Team Foundation Server product team.
The first video focuses on upgrading the core components of Team Foundation Server, including the database.
A second video focuses on how to upgrade process templates which were created using an earlier version of Team Foundation Server to take advantage of the new capabilities.