The search engine optimization process is at the core of all the research and study we do at jWAG. Everything comes back to the "basic" SEO techniques. The problem is that those "basic" techniques change from day to day with the whims of Google, Yahoo and Bing.
It seems like the meta description as an SEO metric is being phased out. Just 1 year ago, we were able to test changes in SERPs ranking simply by changing the meta description of a page. But in the past 6 months our testing shows this doesn't work anymore.
Usefulness of meta keywords went the way of the Dodo Bird in the late 90s. Just like the Dodo Bird's inability to fly, it seems that meta descriptions now have inability to carry any SEO influence within the search engines.
Meta keywords and Dodo Birds became extinct shortly after people started exploiting them (we could probably keep this analogy going on for a while longer). However, we don't see the meta description going extinct any time soon because they are important for getting human attention on the SERPs, just like a good ad.
That was important, so let's say it again...
Meta descriptions have lost their usefulness for SEO and should only be used as an advertisement, as in a short sales message that entices someone to click.
The SERPs from the various engines only show 150 or 154 characters. We like to tell people to just keep it below 150, and explain what's really on the page. Don't just list keywords, and don't waste your time writing more than 154 characters because no one will EVER see it.
Be creative and include your telephone number, or an asterisk * character to catch someone's attention.
No matter what, the best method of getting the click is simply to say exactly what's on your page, or how the page solves a problem or answers a question.