We've just switched from CVS to Subversion for our .NET development. We are also planning to migrate our document repository from cvs to subversion as well. Its so much nicer using the Windows Explorer extension Tortoise than TkCVS which we are using now (or WinCVS for that matter).
I know you can get Windows Explorer support for CVS, but the features of subversion (like renaming files and folders and moving files and folders between directories and browsing the repository without having to suck the whole thing down) along with the Tortoise UI make it a compelling replacement.
What are you using for Visual Studio integration?
A while ago we found a Russian company called PushOK (www.pushok.com) who provided an SCC plugin for Visual Studio for CVS. This plugin was far superior to any other plugin that we had found and only cost US$19. Luckily, these guys have recently released a beta version of their plugin for SVN. We've started trialling that for our source control and so far its looking good.