I wrote posts when we hit 1,000,000 files (Nov. 18, 2005) and 10,000 changesets (Sept. 26, 2005) on the DevDiv server. When you look at the April 2007 statistics (April 18, 2007) for that server, we're at 77,658,652 files and 204,556 changesets. Clearly, that's a huge change in roughly 18 months.
The file count climbs dramatically every time we add a new branch. A full branch has about 3 million files. Normally, we add a partial branch (1 - 2 million files). So nearly all of the growth in files comes from creating new branches.
The increase in the number of changesets is largely due to a tool listed in the table at the end of Brian's post. There's tool called SyncDepotToMaddog checks in changes to TFS whenever changes are made in Maddog, which an application used by the QA folks. It checks in a lot. The changesets weren't going up nearly so fast until that thing was unleashed (quite a while back).
If you are wondering where the application name comes from, we set the user agent string in the HTTP header for each web request to be "Team Foundation (<exe name>, <exe version>)" so that it is recorded in the TfsActivity database (tbl_Command). You can read about how to use it in this post and that post. We have the turned on for the DevDiv server, and that's what Brian uses to keep track of the requests and look for performance issues.