FranticFish - 4:29 pm on Feb 18, 2010 (gmt 0)
Depends on the niche perhaps. If you have a blanket 'no links' policy then fair enough. But I don't think you can say with certainty that it's always spam to link to your site.
It could be a great answer to the question, or an interesting point of view related to the topic being discussed, or a set of data. And if you are a regular trusted member of the forum then why not get some payback for that?