As others have pointed out, TFS gives you a lot more features then SVN does in the form of project management and such. Having used both, and worked with very large companies in implementing TFS, here's my two cents.
1) If you are using TFS 2005, upgrade to TFS 2008. You'll thank me. There are a ton of improvements in TFS 2008 that make it workable.
2) If you live in Visual Studio and you want the IDE integration, go with TFS. I've used SVN integration and almost always drop back to using TortoiseSVN.
3) If you like the idea of accounts being integrated with Windows Authentication, go with TFS. The manageability from that end is nice. There may be hooks for SVN - I'm not positive, but if you like the GUI driven management, TFS is hard to beat.
4) If you need to track metrics or have easier ways of implementing things like check-in policies, go with TFS.
5) If you have people who won't implement it if it isn't MSFT, go with TFS.
6) If you do more than just .NET (Java work, Eclipse, etc) go with SVN. Yes there are very good products out there (like Teamprise) that work well with TFS. But unless the other languages are a small part of your shop, just stick with SVN.
Outside of that, the SCM features of both are about equivalent. They both do branching and merging, the both do atomic check-ins, they both support renames and moves. I think for people just getting started with the branching and merging concept, having the branches be visible in Source Control Explorer is nice.
TFS really isn't that expensive ($1200 maybe?). Compared to SVN it is, perhaps. The integration to reporting services and SharePoint is nice, but again, if you aren't using that, then it doesn't matter.
What I'd say is to download the 180-day trial of TFS and give it a go. Run a trial side-by-side. I think you'll be happy no matter which way you go.
