Executive summary: Read about svn merge --reintegrate and weep.
We waited long for subversion 1.5 to come out. It was hyped to have proper merge support and thus be a real step forward for cvs users. Actually we were using cvsnt which already had some merge support until they broke part of it, and we kept using a patched version.
Anyway, 1.5 finally came out this summer, and since we did not only want to keep having merge support but the history-preserving renaming of subversion as well, the step was done. (We were not migrating but only using svn for new projects.)
Then I started reading the updated svnbook, and wondered: Why on earth is there an option --reintegrate? It turns out that you can only open a feature branch and merge repeatedly into it, to keep it in sync with new stuff on the trunk. But you can only once merge back into the trunk or wherever you came, and then the feature branch must be killed because further merging won't work.
And then it turns out that svn 1.5 was released with this half-working merge support on purpose because it was overdue already and they managed to represent the merge info in the repository in a way that makes a correct implementation impossible, and thusly, it won't happen before 1.6 or so.
And in nearly the same time frame, another star appeared and ran circles around svn in terms of ease of use (just count the number of times you need to type absolute urls in svn command), possible workflows, breadth of utilites. And it's a nice svn client, too.