Well, I've always used the term key'phrases' as opposed to keywords. So, I'm one of the folks using search terms and singular words in metas. I almost never use more than 2...somtimes 3 words in a keyphrase. Also use some singular words...depends on the page I'm building.
Someone a long time ago mentioned that getting traffic on singular terms was much more difficult that 2 or even 3 word key'phrases'...so I use those phrases in the metas...separated by commas.
Oh, and there are differing schools of thought on the use of the separating commas too...that just freaks me out!
