Here's a "gotcha" tip. I have a dev server that had 512 megs of RAM on it. I had the JVM heap sizes configured at 256 meg minimum and 384 meg maximum. Today I added some memory to bring it up to 1 gig. I wanted to change the minimum heap to 512 and the maximum heap to 768. Naturally I set both of them to these new values and hit "submit". I got an error that the "minimum" cannot exceed the maximum. Apparently, the code takes care of minimum first. That means it took my value of 512 and compared it to the "old" maximum value of 384 - causing the error.
To fix this I had to set each value independently - starting with the max value. I set the max value to 768 without touching the Min value. Then I set the min value. I thought that was the end and I went happily to restart the CF service to implement my changes. Naturally the service wouldn't start. I examined the coldfusion-err log in the and it said that I could not start the JVM because I was using conflicting garbage collection switches.
Indeed I had change GC type based on some excellent tips from robi sens blog (from UseParallelGC to UseConcMarkSweepGC). Due to the error (I'm guessing) the system had added the UseParallelGC back into my jvm.config file.
So, if you are going to use the cold fusion admin ap to make JVM changes make sure and backup your jvm.config file (found in the runtime/bin directory on a standard installation).