So a while back Tom Lord, the author of Arch, posted a mail to the arch-users mailing list detailing everything he thought was wrong with Subversion.
Lots of people seem to have agreed with him, to one extent or another, and if you search the web for the phrase 'diagnosing SVN' you can see a number of replies.
Greg Hudson, one of the Subversion developers, has crafted a reply which is well worth reading. In my experience Greg is almost always right, and he seems pretty much right on the money with this one.