Knowing how the search engines actually utilize Meta Tags will obviously help you in your quest for Internet traffic.
Below are the major search engines and a description of what Meta Tags they use and how they use them.

AltaVista
AltaVista is one of the more difficult engines to get listed in the top with. While they do read Meta Tags, you will want to remember that Alta Vista uses a case sensitive algorithm, so typing in Promotion will give you a different result from PROMOTION or promotion.

Excite
Excite does not read Meta Tags, but they do look at the words in the title of your document, so be sure your page uses the most relevant keywords that describe your site.

Google
Google uses only the main text of your document. Try to be a specific as possible at the top of your pages so searchers can see what you have to offer.
To see how Google works look at the 'cached page' on their search results.
Google also places great weight on how popular a website is so ensure you have hundreds of websites pointing to you.

HotBot
HotBot utilizes Meta Tags within your HTML code to their fullest extent. HotBot will score the words higher in their relevancy rating, so use unique spellings or characteristics when describing your site. HotBot also looks at descriptive words in your title and Meta description tags, so use them carefully. As with other search engines be sure that the words you use in your Meta Keyword tags are words that someone would type in to find your website.

Infoseek
Infoseek does utilize virtually all types of Meta Tags, and getting your site indexed in Infoseek is easy. The results of your submission can usually be seen instantly, giving you a good idea of where your site will be listed. As with all of the search engines, be sure that the words you use in your Meta Tags are what someone would type in to find your website.

Lycos
Lycos places more weight in the full text of your document, but does look at your Meta Tags. Definitely use Meta keywords, but make sure you repeat those words again at the start of your document.