Doesn't it depend on what is behind the bookmarklet? In this case the bookmarklet is launching an application within the web page the user is browsing. Does it matter that the (BigTweet) application is "mobile" rather than at a fixed web site?
Granted, the current functionality is nothing that I would expect anyone to pay for.
As an example, what if the bookmarklet happened to open up a full featured word processor with all the bells and whistles? Not sure that you can say that the product wouldn't be worth anything just because the invocation happened through a bookmarklet ...
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.
Granted, the current functionality is nothing that I would expect anyone to pay for.
As an example, what if the bookmarklet happened to open up a full featured word processor with all the bells and whistles? Not sure that you can say that the product wouldn't be worth anything just because the invocation happened through a bookmarklet ...