I use it.
It's down now (Sun Sep 20 20:04:37 CDT 2009) because "Maximum Connections Reached: 4096 -- Retry later" I'm guessing too many people use it. The swingx subproject page is up though https://swingx.dev.java.net/. I must say that swinglabs has never, until now, been down for me. It has always been very slow, but never unreachable.
Swingx recently went to 1.0. People sing java 1.5 should not expect further updates and swinglab's effort is going to be placed in unifying their sorting/filtering with java 1.6 sorting/filtering.