[UPDATE 2/10/2010] You can now get the official Visual Studio 2010 Licensing whitepaper, which also covers TFS, Lab, and IntelliTrace. That is the best resource for understanding the licensing.
Another big piece of news with the release of VS and TFS 2010 betas yesterday is the changes to TFS licensing for 2010 that make it even more affordable. Here are the comments from Doug Seven, our licensing guru in marketing, on Soma's beta 2 announcement post.
Team Foundation Server 2010 will be included in the MSDN subscription that comes with Visual Studio 2010 Professional, Premium, Ultimate, and Test Elements. This copy of Team Foundation Server in licensed for unlimited development and test use (as is all MSDN software) and licensed for one production deployment. These MSDN subscriptions also include one CAL.
Team Foundation Server has three installation choices - Basic, Advanced and Custom. You will be able to install this either on your client machine (very similar to client side SCM such as VSS) or on a server machine just like TFS 2008.
Team Foundation Server will also be available in retail for around $500 USD and will include a license term allowing up to five (5) named users without CALs to use Team Foundation Server. To grow to more than five users, you will need to have CALs for additional users beyond five users. This enables small teams of five or fewer to get up and running on Team Foundation Server for as little as $500 USD.
Of course having Visual Studio 2010 with MSDN means you can get Team Foundation Server up and running at no additional cost.
You can also hear more in an interview with Doug Seven conducted by three MVPS: The Ultimate Announcement Show.
I'm not a licensing expert, so I can't answer detailed questions about licensing. I did want to make sure everyone sees this. It's a really exciting change.
[UPDATE 10/20/09] I wanted to add a clarification from Doug around the CALs and SQL. There is a licensing whitepaper in the works that should be out soon.
Retail TFS does not come with 5-CALs. It has a EULA exception allowing up to 5 users without CALs. The primary difference is that CALs can be used to access multiple TFS instances. A EULA exception cannot. In other words, buying two TFS retail licenses does NOT give me rights for 10-users on one instance of TFS. It gives me rights to two instances with 5-users each. To add more than 5 users, you must have CALs for all additional users.
TFS also still includes a SQL Server license for use with TFS. In other words, you can't use the SQL license included with TFS to do anything other than to support TFS.