New Update (Based on Comments)
As indicated by @kleopatra (core member of the Swing Labs team) the project is dead. Since java.net is no longer available this seems to be dead.
If you still want to use it @emmanuel-bourg referenced this mirror https://github.com/ebourg/swingx and this one https://github.com/RockManJoe64/swingx
Older Update
SwingX 1.6.5-1 is released (actually, a while back, forgot this thread ;), see the announcement in the swinglabs forum. It's a regression release for 1.6.5 which had some painting issues which broke backward compatibility in code build against 1.6.4. The issues were particularly virulent in synth-based LAFs where the synth-installed background painters were ignored, f.i. for JXPanel and JRendererCheckBox. The issues are emergency-fixed, partly by reverting the changes. Future releases are planned to address them more thoroughly.
Update
SwingX 1.6.4 is released, see the announcement in the swinglabs forum at java.net
Update
SwingX 1.6.3 is released, artifacts available from maven rep (at java.net), most probable (we didn't get any alerts :-) from central as well
Original answer
unforunately, the project accessibility suffered badly from the migration to kenai infrastructure - and that starting from a low level, as far as working links are involved. In particular, SwingLabs.org rarely ever was up, and everything there is severely outdated.
To get hold of build artefacts, all releases are available from the project's download section
http://java.net/projects/swingx/downloads
(note the description of the file "downloads-broken-due-to-migration-crap ;-)
EDIT:
for your convenience (and since it seems difficult to c&p from the description of the file above ;-) the link for a bare-bones view of the download section is, then navigate down to releases
http://java.net/downloads/swingx/
The project itself is alive, a milestone release in the wings - hampered again by infrastructure woes, as described in
http://www.java.net/forum/topic/javadesktop/java-desktop-technologies/swinglabs/latest-swingx-demo-other-stuff
Sorry for the mess, not overly much we can do right now (or in near future)
Jeanette
