Handling multiple merges onto branches in Subversion or CVS is just one of those things that has to be experienced. It is inordinately easier to keep track of branches and merges in Mercurial (and probably any other distributed system) but I don't know why. Does anyone else know?
My question stems from the fact that with Mercurial you can adopt a working practice similar to that of Subversions/CVSs central repository and everything will work just fine. You can do multiple merges on the same branch and you won't need endless scraps of paper with commit numbers and tag names.
I know the latest version of Subversion has the ability to track merges to branches so you don't get quite the same degree of hassle but it was a huge and major development on their side and it still doesn't do everything the development team would like it to do.
There must be a fundamental difference in the way it all works.