Once the volume surpasses decent threshold, the UX would be quite difficult to build without some sort of complex grouping or intelligence. The key to a successful unified inbox would be learning what is "important" to each user and customizing the experience accordingly. Otherwise, people would start ignoring busy twitter feeds and focusing on individual emails, IM's, etc, which they could achieve by simply opening each service in a separate browser tab.
Agree completely. It would be possible to abstract away all of these services into a common dialect (so that grouping and filtering works across multiple services) and then let the user "build" different UX approaches by allowing one to group and filter different sources into specific view: ex, group tweets and irc messages and have that group display only some UI stuff, group rss/fb posts and have the UI display some other stuff.
