<meta name="Description" content="Get your site on the first page of Google, Yahoo and Bing too, using simple seo. Call us on 0845 094 0839. A company based in Scotland." />
Make it relevant to a query and write it for humans, not search engines. If the keyword phrase is present in the meta description, you can usually depend on the meta description showing in Google listings.
Google looks at the description but there is debate whether it actually uses the description tag to rank sites. I think they might at some level, but again, a very weak signal. They certainly index it for snippet use, not so much ranking pages though.
Some times, I will ask a question with my titles, and answer it in the description, sometimes I will just give a hint;
It’s also very important in my opinion to have unique title tags and unique meta descriptions on every page on your site. It’s a preference of mine, but I don’t generally autogenerate descriptions with my cms of choice either – normally I’ll elect to remove the tag entirely before I do this, and my pages still do well (and Google generally pulls a decent snippet out on it’s own which you can then go back and optimise for serps ;).
Sometimes I think if your titles are spammy, your keywords are spammy, and your meta description is spammy, Google might stop right there – even they probably will want to save bandwidth at some time :)
Putting a keyword in the description won’t take a crap site to number 1 or raise you 50 spots in a competitive niche – so why optimise for a search engine when you can optimise for a human? – I think that is much more valuable, especially if you are in the mix already – that is – on page one for your keyword.
So, the meta description tag is important at some level in Google, Yahoo and Bing and every other engine listing – very important to get it right. Make it for humans, with the keyword phrase present.
Oh and by the way – Google seems to truncate anything over 160 characters in the meta description. actually, might be just under 160 now, so keep meta descriptions to about 155 characters to be safe) :)