Digg founder Kevin Rose's "IM competitor" startup that was hyped on Digg two months ago has been introduced, and it appears to be a Twitter clone with support for posting files. It's named Pownce, and it calls itself "a way to send messages, files, links, and events to your friends."
It's invite-only right now (I'm on the waiting list), so there's not much information available about the app. Leah Culver (Pownce developer) has blogged about Pownce here, but doesn't really add any information not on Pownce's about page. (Viewing her Pownce profile page does give some insight into how the service may work.) As is standard operating procedure with Web 2.0 startups, there's a Pownce blog (currently content-less save for the requisite Hello World post), which I'm sure will be the best place to watch for updates on Pownce's progress.
It will be interesting to see what becomes of this site; it's got a big advantage over any random startup since it will undoubtedly be splashed all over Digg due to Kevin's involvement, but we'll see if it's able to make the jump from being popular with Digg fanboys to being popular with the average Web user.