Description meta tag, effective or useless?

honestly, i really don't know whether it is still effective or not, but IMO, there's nothing wrong in placing meta tags. at least it gives people an idea of what the site is about before clicking it.

whether it has advantage or not, there's no harm in placing it

Rand at SEO Moz included a interesting tidbit in his post on What Separates Search Marketing Novices from Experts:

Rand Fishkin wrote: I see a great number of sites where the meta description tags are either copied from page to page (i.e. non-unique) or contain only the first 2-3 sentences of the page's content. The former's issue is obvious, while the latter is unwise because the search engines will show whatever content is most relevant to the user's actual query if you provide no meta description, and thus you'll almost certainly get more long tail search clicks by letting the engines supply your description. The exception is if your intro sentences are excellent descriptors of the content on the page, which is sometimes the case with certain article sites or blogs.

So, in order of preference you would have:

1. Unique custom meta description that includes keywords and encourages click-throughs (by far the best option)
2. No meta description
3. Description copied from first paragraph of text (often done in blogs, forums, and other CMS's where you can't supply a custom meta description)
4. Description same as other pages on the site

Google does seem to do a pretty good job of pulling in some relevant text when there isn't a suitable meta description.

This article from HighRankings.com has some good info:

Quote: In this case, I don't have the phrase "SEO copy" in my Meta description tag, nor is it anywhere on the page as a complete phrase. Because of this, Google has simply found instances where the word SEO and the word copy were near each other, and used the surrounding text as the snippet. (answers my last question)

Now, if I felt that "SEO copy" was a viable keyword phrase that people might be searching on, I may want to adjust my page accordingly so that the phrase appeared in my Meta description tag as well as somewhere in the body text. Again, this is not because it would help it to rank highly, but because I would receive a more suitable description that was more in tune with what the searcher was looking for. One can surmise that they might be more inclined to click on my listing in that case.

She goes on to say that Yahoo did show the meta description when it could not find the search phrase on the page.

This page also has a good quick & dirty summary of how Google builds descriptions:

http://www.stonetemple.com/blog/?cat=17

Ooh, helpful wordpress info there!

Just on some quick experimentation - it seems that google is sometimes using the meta tag completely, other times just page text snippets, and sometimes a combination of both. ON this search for example:

http://www.google.com/search?client=opera&rls=en&q=when+google+show+meta+description+or+page+text&sourceid=opera&ie=utf-8&oe=utf-8

(googled "when google show meta description or page text")

The first result shows only snippets of page text. There is a meta description, but my keywords did not appear in the description.

The second result shows the first part of the meta description, up to the ... the rest is from the page text. (Keywords did appear in the description)

For the third result, there is a meta description but again, it does not contain my keywords, so Google found them on the page instead.

The fourth result is interesting - "Meta Description" did appear in the description but only at the very end. The description is very general and not very useful. Google showed snippets of page text.

The fifth result also has a very generic meta description (no keywords), google used page text.

The rest of the results on the first page were the same - the meta tag was either not there or generic to the whole site, so google showed the words instead.

Hypothesis: I think what happens is that google looks for the keywords starting with the meta description. If they appear in the description, it will show at least part of it. If they do not, it will find them on the page and show that instead. It makes sense - seeing something with their keywords is most helpful to users. If the page has a well written and descriptive meta tag that's probably the best thing to show, but it seems that most sites don't. And it is hard to generate good meta tags when you're using any kind of CMS.

So, to answer the queston: Yes, it is very important to have a good meta description at least for your home page. Make sure it includes the generic keywords you are targetting and encourages users to visit you.

Next question: how does Google decide which keywords to show? If you knew that you could intentionally write your text to include your keywords in certain strategic places that would encourage click-throughs.

I agree, some bots read the site meta tags and some bots value them pretty high... As I also read somewhere as Megan mentioned, it's seems useful in differentiating duplicate contents on pages...

I voted that it's important just because it might be seen by human visitors on some searches. It could make the difference between someone clicking on your link or someone else's. And you can control what goes in there.

I'd like to know how google decides whether to show keyword text or a meta description. I'll have to investigate that further. It seems to me that they might be doing that when there is no meta tag...

I've also heard that meta tags could help with duplicate content filters - if you have unique tags on each page they mark the page as being unique.