This is one of those problems that make an otherwise intellgent person feel kinda dumb...like I half-anticipate Jamie will come on here with a simple answer and i'll slap my forehead but here we go:
I've gotten pretty good at listeners but taking my first crack at postfunction "canned" script and got some serious head-scratching going on here. First,
the script examples includes a helpful object "com.onresolve.jira.groovy.canned.utils.WorkflowUtils" to pull out params like this:
WorkflowUtils.getUser(params)
Unfortunately, adding the groovyrunner-2.1.15.jar to my <jira>\atlassian-jira\WEB-INF\lib and my IDEA class library does not resolve anything in the "utils" namespace? Even though those classes are clearly there and clearly in the library list in IDEA. See the short clip for proof I'm not crazy. 
http://screencast.com/t/3yvGe8GMC
Additional bonus question: I've had to grab the latest groovyrunner-n.n.n.jar out of my plugins directories because I can only find incidental references to that jar file online and they're all out-of-date. Is there a standard location to download the class libraries? (and source jar would be awesome too)