Also having a formatting bar (for bold, italics, blockquotes, strike through, read more, etc.) would be cool as well (e.g. look at the LiveJournal.app to see what I mean).

If you have all of those features–plus the ability to insert images where ever (instead of having them all inserted at the bottom) then this would become a killer app for me!

Of course if you are going to add that, you should also look at adding support for Akismet management

I think push notification opens up some really interesting possibilities such as the one you described.