tedster - 3:17 pm on Apr 2, 2012 (gmt 0)
There are... but the target we're studying keeps shifting, so older studies no longer apply. In fact, there is some evidence that it has shifted again recently. The meta description apparently had no direct effect on ranking for several years, but now in one recent study (too small to be 100% conclusive) it looks like the meta description can impact relevance.
I've worked with sites that were doing quite well with no meta description - and adding one seemed to make no difference. The question here: are there other relevance signals that are so strong that the meta description becomes a "reinforcing signal" but doesn't add any boost to the rankings?