One of the biggest things that I'm interested in, is being able to use Google checkout. If they can provide an easy API integrated to their hosting, it's going to be killer.
That's what I heard in conversations with several people. For my application (ezLearnz.com), I'm really interested in using google documents instead of rich text fields, since that solves a whole host of problems (adding images, revision history, sharing editing capabilities, etc). But I think that's a ways off.
