The last post was on Description Tags - 7 Quick Steps to Success. While that post covered some basic things to make the most of your description tag it would be good to cover/emphasize another thought that could have an impact on the success of your description tags.
#1 Question: Hey, we did everything you said to optimize our description tags & Google is showing a lame strange snippet from our site- What's going on?
Good question. Here's the answer in short: Google may totally disregard your hard work in creating compelling description tags and put whatever they want there. Why?
Google's number one goal is to return the most relevant results to their audience, and because of this they may pull content from other portions of your page to better match the keywords used in the searcher's query. Think about it- If you have a page on your that talks about gluten-free pasta you can likely only target one or two keyword phrases message in your description tag such as "gluten-free pasta" or "wheat free pasta". Likely if the searcher types in those keywords the description tag you wrote will come up. But if they type in "gluten-free spaghetti" Google may crawl that page and see that you indeed do have that phrase on the page and put together their own description tag/snippet to best match the searcher's query. Here is Google's description with underlining and bolding added by us:
"Google's creation of sites' titles and descriptions (or "snippets") is completely automated and takes into account both the content of a page as well as references to it that appear on the web.
We use a number of different sources for this information, including descriptive information in the META tag for each page. Where this information isn't available, we may use publicly available information from DMOZ. While accurate meta descriptions can improve click through, they won't impact your ranking within search results. We frequently prefer to display meta descriptions of pages (when available) because it gives users a clear idea of the URL's content. This directs them to good results faster and reduces the click-and-backtrack behavior that frustrates visitors and inflates web traffic metrics.
While we're unable to manually change titles or snippets for individual sites, we're always working to make them as relevant as possible. You can help improve the quality of the snippets displayed for your pages by providing informative meta descriptions for each page."
What does this mean for you?
Does this mean you should just give up and not write meta descriptions? No because in many cases Google will show your description for the search query. But if they don't it basically comes down to what you should be doing already. Having great content on your page, perhaps having keyword variations and well written copy so that if Google does show something different it will still be relevant.
More information on meta descriptions/snippets and how they work:
Excellent article by Ken Lyons: Meta Description Mutiny! Take Control of Your Text Snippets
Official Google Video with Matt Cutts discussing descriptions/snippets: