At work, I'm on the brink of moving our code base from an Ant / CVS build environment to a Maven-mangled^H^H^H^Haged / SVN world.
This means I'm about to lose a few years worth of history - and on my particular product this history is extremely valuable. I looked around for a tool that would retroactively merge CVS ,v files (aka rcsfile(5)), but I couldn't find any. To be honest, I wasn't really sure what to look for.
So I spent the day hacking together a tool that merges two ,v files together. It doesn't work on binary files, it doesn't work on Windows and it may not work for you, but it does the job I need.
Here it is: cvsblend-0.1.tar.bz2 - needs Java 5, comes with source, proceed with caution. Let me know if it helps you out.