Gentle reminder: there's a history page in the SwingX wiki
The idea is to have a place where all major changes (read: everything that'll require users of the framework to change their applications or open up new opportunities of usage) are documented. We (yes, including myself ;-) severly neglected that page since ages - the (mine at least) initial excuse was that the place is not safe as we lost content when java.net had been hacked a while ago. That will not happen again (haha ... me believing Sonya and the new drive brought about by Snoracle).
So let's continue - all developers should leave a line on relevant api changes (including cleanup due to removing deprecated code). And all users of the library are dearly welcome to fill the gaps if one of the committers forgot to document anything - after all, it's a wiki :-)