If the first few lines of your page provides a good summery this tag need not be used The length of the tag Should be kept as short as possible. Many engines ingnore the tail of the tag if it is too long. Altavista claims to index upto 1024 bytes, but I have yet to see a description that long in my searches. It's a good idea to keep the description to less than 200 bytes. Is used to provide a list of comma delimited keywords for the benifit of search engines.
Many engines ignore the tail of the tag if it is too long.
Altavista indexes upto 1024 characters, but with other engines it is low as 200 - 250 Eliminating between two keywords helps to keep the size of the tag to a minimum Add synonyms to the keywords tag. For example if your page is about hard disk drives, ad the keywords hard drives,hard disks,hard disk drives,fixed disks,fdisks and winchester. Some engines may consider repeated keywords as spam and will penalise you by not including your page in the index. Search engines do not indicate on their help pages the maximum allowed number of repititions. Many suspect this to be six for some engines.