To do paid serials well, Smashwords would need (in my VERY humble opinion
) to rework their site. I can see why Mark's unenthusiastic, from that angle.
On the other hand - I can see that there's a potential for a great service here.
Mark, my darling, keep in mind that wandering onto a forum mostly made up of people who read ebooks, to ask about serials, is a bit like going to a fishing forum to ask about revoking fishing rights. Well, it's not completely analogous, but you get my point, right? If you went to the forums at webfictionguide.com and asked the same question, you'd get an overwhelming vote FOR serials, I think.