I've seen the Mailplane.app and it rocks. Perhaps there's still time for Flock to find its way, again. (Unrelated to this post, last update to Flock on my G4 iMac made the thing run so slow it was painful... just sucked up the resources like a Dyson.)
Clearly something is going on here, and when measured against Microsoft’s Silverlight and Adobe’s AIR frameworks, we’re starting to see the emergence of an opportunity that I think will turn out to be rather significant in 2008, especially as an alternative, non-proprietary path for folks wishing to develop richer experiences without the cost, or the heaviness, of actually native apps. Yes, the rise of these hybrid apps that look like desktop-apps, but benefit from the connectedness and always-up-to-date-ness of web apps is what I see as the unrecognized fait accompli of the current class of stand-alone, standards compliant rendering engines. This trend is powerful enough, in my thinking, to render the whole discussion about the future of the W3C uninteresting, if not downright frivolous.