While I don’t currently use OpenNMS, I do lurk on the mailing lists to learn about it 🙂
While on serverfault today, I thought about checking to see what OpenNMS questions there may be, and found several. None I’m qualified to answer, but the results are here: http://serverfault.com/questions/tagged/opennms.
For posts that merely have OpenNMS mentioned: http://serverfault.com/search?q=opennms.