I've been following with interest the path Microsoft are making with Windows Mobile 5.0 and after owning a 02 XDA IIs and now waiting for my 02 XDA Atom to arrive...I wanted to see what they see in the future for these devices.
This article on Pocket PC Thoughts is a good overview of Steve 'crazy' Ballmers keynote.
They used the Atom to demo Microsoft Powerpoint Mobile connected to a projector via Bluetooth to display a presentation.
My main usage of my PDA is as a phone with contact information synced with my laptop. Along with SMS (unlimited messages and backed up to laptop), Tasks, Notes (both text and drawings), MP3 player and a MPG player for watching the latest Smallville, 24 and movies on the way to work!
I hope to be able to soon use it as a decent camera too. I'm yet to think of a killer app for it, but really no point just yet until it is more mainstream and is in the hands of people who are given them free on contracts. More than likely this will be to do with instant messaging and file sharing (photos, music etc.).
A decent RSS reader synced to Googles Reader would be handy...AvantGo is very good but isn't free.