We are a mostly MS shop at work doing .NET LOB development. We also use MS Dynamics for our CRM app... all the devs are currently using VS/SQL Server 2008. We also use VSS, but
We are a small development shop, and decided that Team Foundation Server carries too much overhead for us. We used to write custom MSBuild scripts to run from the command line, but after we discovered TeamCity, we moved our entire build process over to it.
We've found TeamCity to be easy to use and configure, and JetBrains provides excellent support and documentation. They are also on a much faster release and update cycle than Microsoft.
Their support for SVN source control is excellent, and we like the fact that they support both MSTest and NUnit for unit testing.
We also liked the fact that the TeamCity Professional edition was free, so we could evaluate it to see if it worked for us. We haven't hit the number of project configurations (20) that would require us to upgrade to the Enterprise edition.