When one asks for computation of retained size, the profiler shows modal dialog. While I can understand you don't want the user operate with the heap snapshot, showing a global modal dialog prevents me to do any other action with the IDE like working on other bug meanwhile.
Given the fact that computing retained size may take minutes and the dialog cannot be closed, I consider it as an important UI responsiveness blocker.
Btw. "show nearest GC root" also shows modal UI dialog, but at least it does not take that long to compute.
Fixed in profiler-main
user: Tomas Hurka <email@example.com>
date: Tue Nov 20 17:27:53 2012 +0100
summary: bugfix #221654, get rid of modal dialogs in computing GC roots and retained sizes
Integrated into 'main-golden', will be available in build *201211230002* on http://bits.netbeans.org/dev/nightly/ (upload may still be in progress)
User: Tomas Hurka <firstname.lastname@example.org>
Log: bugfix #221654, get rid of modal dialogs in computing GC roots and retained sizes