I don't remember seeing it posted, so I though I'd mention that on two sites (not paid ones) that don't have a meta description tag, the actual page titles are being used at alltheweb.com but it's the ODP description that's being shown. It doesn't appear to adversely affect it, but the keyword, if it's in the ODP description, is being bolded. Not so with those at Lycos, it's part of the page itself being used.
Also, I noticed clustering with a site that has one interior paid page, with the index page coming up instead of the paid one for the main keyword. For a couple of interior pages that are unpaid, it's the pages themselves showing - understandable because those keywords don't come up in text on the main page. I was a little surprised to see it done that way. Same on Lycos, with the same ranking.