Every one of your web pages should have a unique (to the others) title and description which is relevant to each page`s content.
While not all search engine use the description tag, Google does.
I have heard a lot of guys saying Meta Keywords tag is useless, but first time heard that the use of (all?) meta tags is debatable. What about the `description` part? how would search engines describe the web pages without it? Okay, there is no hard and fast rule that Google or any other engine would ONLY rely on content in `description` tag.
But smart optimisers tend to squeeze in most relevant site summary incorporating primary keywords in their `description` tag.Basically you are suggesting search engines what`s the best summary of your page. So invariably best optimised sites tend to get their `desricption` part picked by search engines, rather than random chunk from <p on the web page. Its too risky to leave out a badly written `description` tag. I`d rather have nothing there and write strong page copy, as Nikole says, but then you`d have to rely on search engines`s to pick what chunks they pick.