If the system is hung such that you can't get Activity Monitor to sample, use command-option-control-shift-period to run sysdiagnose. Attach the resulting /var/tmp/sysdiagnose_$(TIME).tar.gz to your bug report.
And inside that tar.gz file is a spindump.txt file, which will have the samples of whatever application is spinning at the moment, just like if you used Activity Monitor to sample it.