Below is a comparison of Source Safe and Subversion.
Visual source Safe (VSS)
Commits are not atomic.
Commits are atomic.
Renames affects the whole history.
Renames are supported.
Only supports locked checkouts.
Shared checkouts are default but supports locking.
Permissions are supported but anyone can access shares and mess up files.
Permissions are assignable to granualar level of folders.
Smallest commit block is a file.
A line is the smallest commit block.
Works only on Windows shares making hard to go through routers.
Supports sharing via http and https using apache.
Works only on Windows, which is bad for obvious reasons, but this also makes it very difficult to automate testing.
Works on Windows, Linux, Unix, OS X, and also Java which makes it ultimately portable. Can be used via SSH (easiest setup).
Viewing file status is very difficult.
Viewing file status is very easy.
Merging conflicts is very simple.
Proprietary and has hefty licensing fees.
Open Source and free.
Most of the above was taken from: http://aspxwizard.net/blogs/wand/archive/2007/11/13/subversion-vs-source-safe-vss-vs-svn.aspx