Garbage First (G1) garbage collector http://weblogs.java.net/blog/opinali/archive/2009/02/here_comes_jdk.html
Do you think this garbage collector is better for JRun, running ColdFusion 8?
I will tell you that updating the JVM in ColdFusion is a breeze, so I always update to the latest JVM once it's been released for a month. I haven't had any problems with any of the releases thus far and ColdFusion seems to be getting a little quicker with each update.
That said, you should always updated the JVM on a test machine first and run your battery of tests to make sure nothing breaks.