Thanks for the comment, and the props on the post! I totally understand your point, and somewhat agree- small businesses pressed for time should first get set up on the "mainstream" social networks most relavent to their business (which might be Pinterest, depending on their user demographic). Having said that, a few thoughts:
a) It doesn't take much to set up a shingle on Pinterest. Once you're set up, it's relatively easy to update without too much effort or interaction.
b) Point "a", when coupled with the site's robust engagement and conversion numbers, would suggest that it is a smart move to get set up on Pinterest, at least as a beta test.
c) Admittedly, we don't know what direction the site will go. All of the major social networks started out small. What we do know is that the consumer adoption of mobile devices favors visually-oriented networks and easy touch-screen actionability. Pinterest provides both.
Thanks again for your comment and insight!