Since the term was first coined in february by James Garrett there seems to be a mania to convert each and every site to ajax. Though google showed the way by using ajax in gmail, it's only now that we are seeing some real good applications made in ajax.
You can find a good list of new and upcoming ajax apps in a compilation by Dan Grossman here and here. Out of them meebo and writely seems pretty new and innovative.
Well, what took so long for ajax apps to pick up. May be increasing reach of broadband which has made loading even ajax apps pretty fast, coz even now if the u hav a li'l less bandwidth than gmail fails to load. Then thrs the advantage of just opening a browser and launch the app instead of downloading a appication and installing it. The first generation of ajax apps is all about personal management as in calander, todolists, contacs, email, IM. Still i feel ajax is in it's infancy and there will be more innovative apps we r goin to see in near future. Soon we'll be seeing apps with a gr8 degree of consolidation. Like yahoo seems to be doin in it's beta mail.
I see a imminent war in whr u have a online desktop in ur browser. Either it'll be yahoo desktop or google desktop or micorsoft desktop(doubtfull, who'll buy office ;))
Seems like flash is also getting a upgrade from irritating ads to full sites and applications in goowy.