No, the medium is intrinsically wrong. Bookmarklets are easy to copy for free. Perhaps if your bookmarklet led to or interfaced with a fully fledged application, people might be willing to pay for the application - but then the bookmarklet is mostly irrelevant, or at the least is not the central appeal, much like del.icio.us's toolbar is omnipresent and yet not presented as the navel of the application.

I maintain - no one will pay for a bookmarklet, so a website that starts with "we provide a bookmarklet that..." is doomed to remain a hobby.