Is there any problem with using a varchar type for a primary key (in terms of efficiency, etc.)?

no, not really

Cool; primary keys can be descriptive.

Yes, in which case they are frequently referred to as "natural keys". The corollary would be "surrogate keys", which by definition convey no information about the record they represent.
My God. I am embarrassed to admit it took me three attempts with the spell-checker to spell corollary correctly.

It took me one attempt to look it up

pootle flump ur codings are working excelent.

Depending how you define efficiency, the specific nature (maximum length for example) of the primary key data, whether or not you use it in foreign keys and also what you propose instead of the natural key, there *might* be a "problem".

But Rudy is quite correct - there's nothing inheritantly wrong with varchar PKs.

pootle flump ur codings are working excelent.

I appreciate this information. Re. the spelling... remember, the more we know, the more we can forget (apology of a geezer... though not to imply that anyone but me is a geezer...)

varchar keys aren't necessarily natural keys

and the word you were looking for, blindman, is opposite, not corollary

(apology of a nitpicking geezer, or a picnicking teaser, or ... )

These primary keys that I'm talking about will have short max lengths -- VARCHAR(6) ... or something under (10), whatever they might be.

Re. opposition and corollary, an opposition can be offered as a corollary.... a lovely case of non-conflicting apposition.

Actually, I think the most appropriate term would be "complement".