I think they tend to just ignore the keywords tag anyhow so put as many as you like in there.

That said, some people do put too many keywords in their keywords tag, it looks silly and just tells competitors where they may be placing their efforts in the future.

Search engines today ignore the meta keywords tag completely.

The meta description is not used for ranking purposes (in Google at least), but it may be used as the snippet below the title in the search results. If it is too long, it either gets truncated or replace by test chosen from elsewhere on the page.

The title that displays in teh search results seems to be limited to about 70 characters - but if it is longer, the rest of the tag just doesn't show. Sometimes if the tag is slightly longer and the user searched on a keyword that is at the end of the tag, the search engine will replace part of the middle area with three dots - an ellipsis. So this indicates that characters running slightly longer in the title element will still be scored for ranking purposes. It's something you can test. Some people recently tested and showed that at least 83 characters will "count", although the ellipsis will display.

There doesn't seem to be any penalty for being slightly too long in any of these cases.

epkgupta"

I was reading something the other day and I forgot where, but it goes along with what "tedster" and "Mark_A" say.
The other thing I noticed was the statement that <title> tags up to 256 characters are being indexed.
Now, will someone verify that for me please.