My co-worker, Greg Sabino Mullane, noted this writeup on the MarkMail blog comparing the amount of traffic on the various MySQL and PostgreSQL mailing lists.
I suppose you could pessimistically say that PostgreSQL users need more community help than MySQL users do, but reviewing the content of the traffic (and going from years of personal experience) doesn't support such a view. The PostgreSQL community seems to have more long-term, deeply involved users who are also contributors.
But let's hope the competition in the free database world picks up. It looks like the new Drizzle project has a good chance of growing a new community around MySQL.
In any case, the MarkMail mailing list archive and search service is an excellent resource. Thanks, MarkMail folks!