That doesn't mean that if you use 999 characters that all the search engines will include all of your keywords-all 999 characters. Infoseek only uses up to 744 characters while AltaVista uses less than 500. Do not repeat any keyword more than three times. The search engines consider this spamming. If they catch you doing this, they won't index your site at all.
Some search engines are case sensitive.
The description must be less than 150 characters. This is what the search engines display when they index your site. Use a few of your very most important keywords in your description. Avoid using commas in the description. Don't rush when you are creating your Meta Tags.