Running Super Elvis under 1.5beta1 and 2, with the following parameters:
-Xmx24m -Xms24m -XX:MaxGCPauseMillis=2 -Xincgc -Xconcgc
I get this printed out over and over and over and over:
Java HotSpot™ Client VM warning: Mark stack overflow in CMSKeepAliveClosure
Cas 
Well, all I know is that -Xincgc uses the Concurrent Mark Sweep collector as of 1.5… thus the ‘CMS’ in CMSKeepAliveClosure.
Ah, this is already in the bug database:
http://bugs.sun.com:80/bugdatabase/view_bug.do?bug_id=5053106
Looks like it should be fixed in the next beta 3 snapshot.