As stated on its website, VisualSVN is a plugin for Microsoft Visual Studio for seamless integration with Subversion.
This is an early review since I've been using it for less than a week. Many think to Scott Bellware for making me aware of this product because it has made my day just a bit easier. Up until now I've been using TortoiseSVN, a windows shell extension, for my integration with our Subversion source control repositories.
VisualSVN wraps TortoiseSVN and makes all the commands available from within Visual Studio 2003 or 2005. I'm using VS 2005, so I have not tried it with 2003. I am very pleased with my experience so far. VisualSVN puts a colored diamond next to each file (green/yellow/red for unchanged/changed/conflicted). I can show a diff, revert, etc from the solution explorer. I can also update commit either from the menu or the Solution root. The user experience is the same as Tortoise since VisualSVN doesn't introduce a new way to update/commit. VisualSVN actually pulls up the TortoiseSVN window for update/commit. TortoiseSVN is actually doing the work, but VisualSVN pulls in access to it into the IDE. This takes away the need to switch back to Windows Explorer for source code interactions.
In short, I'm very impressed with my trial so far, and I plan and laying down the $19 for the great tool. After Christmas, they plan on setting the price back at $49.