Which makes me realize that I haven't seen any Twitter clients allowing you to filter out tweets by app. The info is provided through the API, so it'd be pretty easy to do.

(NB: I haven't tried a whole lot of client so that might be out there, it's at least not very common)

Second thought on the subject: what identifier will tweets from iOS have? It sounds like iOS will have Twitter at the OS level, so it's likely that it will be the same client ID/name for all tweets regardless of if they're coming from Safari, the Photo app or anything else. In fact, the keynote made it look like you needed the official Twitter iOS app, so it's likely to be that app ID/name.