After a repository is imported from VSS to SVN, there are some files which I guess might be VSS specific - .vsssc and .vssscc files for the solution and .vspscc for projects. They seem to be related to VSS project binding. Are they needed (or useful) for SVN as well?
There is also cruft in the solution and project files. See this great page from Alin Constantin for instructions.
The .vsssc and .vspscc files contain references to the visal sourcesafe server in which the solution/project was kept. Subversion doesn't need this information as this information (and more) is stored in the .svn areas of your working copy.
For the data in the .sln and project files it depends on whether you use AnkhSVN, VisualSVN or neither.
AnkhSVN (2.0+) is a real SCC provider and allows (optionally) marking the projects as managed by Subversion (/AnkhSVN). This will add similar SccXXX lines to the project files as VSS did, but will make all projects send information to AnkhSVN.
VisualSVN doesn't mark projects and tries to handle everything from the subversion administrative area by itself.