I've been on bulletin boards for over 10 years now and was a SysOp for the Music roundtable on Genie for years. If there's one thing that experience has taught me, it's that some people are horribly inpatient with topic drift and some can't live without it. My theory is that no matter what the topic, eventually someone is going to make it about music. That's why we come to Mudcat in the first place.
Mudcat will be here so long as people love and are curious about music. AND so long as they are made to feel welcome and there are people to talk to who respond to them.
From my own relatively limited experience here so far, I've noticed two annoyances.
1) People who don't have a name next to "from" who start giving me grief about doing typical newbie things. One thing Sysoping has taught me -- NEVER treat anyone like s/he is stupid. That's the quickest button for a flame war.
2) People who try to drag topics where they aren't ready to go yet, thereby stifling the interaction that IS there [and driving people away]. To nudge is good. To drag is, imho, not.