zby what do you think? Do threads wandering off-topic cause you a problem?

Sometimes, I find this whole on-topic/off-topic thing is missing the point. Just like political correctness, or perhaps Perl correctness ;). Often the most interesting threads are ones which have shifted considerably.

A significant factor is which secion of the monastery the root node is in. SoPW is clearly for questions, OK, yep perl questions, but also questions about perl, camels, Larry's stance on Ada, why not?

As for the other secions of the monastery, meditations and monk discussion, these are even freer in topic range.

In extreme cases, when a topic is venturing into flame warfare, there's always consideration, which can be applied to reply nodes just as easily as to root nodes.

Finally if you think a thread is branching too far from its original root node, post a new root node with appropriate title, and link to the original node.