I wasted a considerable amount of time following the instructions from this page on how to install Subclipse on OS X, trying to get MacPorts to install the right version of Subversion (Why subversion, you may ask? Because a customer is still using it, that's why...).

It turns out that MacPorts doesn't even have the 1.8 version of Subversion - it's only got 1.7, which won't work with the version of Subclipse I'm using. So, I had to go to WanDisco and download it (after removing the MacPorts versions first), and then everything worked.