tedster - 7:49 pm on May 10, 2010 (gmt 0)
That would imply a lot of title optimization ... argl!
And meta descriptions... and page content, too.
Google does a good bit of snippet optimization for you - ignoring the meta description that you provide if their algorithm indicates that it doesn't work well for a specific query.
Same thing applies to title rewriting. Although titles are certainly "adapted" for a specific query a lot less frequently than snippets are, we are seeing more of that in recent times, too. And especially when it comes to snippets, the on-page content is frequently used as the raw material.
It seems to me that monitoring the in-depth WMT reports for your high traffic queries has become a mission-critical task. However, when it comes to user-generated content, especially paginated discussions of almost any kind, it's probably better to let the description selection up to Google and just focus on that title.