This came up before, request to add meta description to forum pages, here
If you have a google webmaster's account they have a section for
"While we were crawling your site, we noticed some issues with the content of your pages. These issues won't prevent your site from appearing in Google search results, but paying attention to them can provide Google with more information and even help drive traffic to your site. For example, title and meta description text can appear in search results, and useful, descriptive text is more likely to be clicked on by users."
and then they list your problem urls under three categories:
Duplicate meta descriptions
Long meta descriptions
Short meta descriptions
So it would be nice if spf covered this and outputted unique meta descriptions for each topic, which at the least I guess could just contain the topic title.