This is just a quick list of Twitter clints I can think of, very rough but its just to help Becca.
Twitterriffic auto refreshes but doesnt have many features - bit old now
http://iconfactory.com/software/twitterrific
Beak - nice new app - refresh every 5 mins:
http://beakapp.com/
Eventbox - does rss news, flickr, facebook and twitter:
http://thecosmicmachine.com/
Tweetie - Very new but good. Currently refreshed every 5 mins, next version can change refresh
http://www.atebits.com/tweetie-mac/
Bluebird - not the best app, but is fully skinable to look how you want:
http://bluebirdapp.com/
Syrinx - http://www.mrrsoftware.com/MRRSoftware/Syrinx.html
Adobe Air Apps: - tend to hog more memory and not as nice as native
Twirl - http://www.twhirl.org/
TweetDeck - http://www.tweetdeck.com/beta/
Destroy Twitter - https://destroytwitter.com/
Spaz- wrong! - http://funkatron.com/spaz/
Toro - http://tinyurl.com/ao8j5q

Apple just game a demo of their new OS for the iPhone, available now for developers and for all versions of the iPhone and iPod touch this summer.
Main features are:
- Copy and paste at last
- Push notification service
- System wide Spotlight search and in app search within key apps e.g. iPod and Mail
- All the normal bluetooth stuff supported
- Stereo bluetooth
- iPod now has the shake to shuffle feature
- landscape mode keyboard
- notes sync to desktop
- Tethering is built in, but is dependent on carrier support
- Developers can add streaming video and audio to their apps, along with in-game voice use
- Video scales depending on bandwidth
- full public API for maps and core data so we can have turn by turn navigation
- In app payments so we can have add ons for games, and book stores etc
- SMS app now replaced by Messaging app, can do MMS
- Send photos, contacts, audio files, and location via MMS
- In Messaging app, can delete individual texts and forward them
- Built in voice memo app, inc edit/trim/share with mms and email
- Apps now have full use of the dock e.g. joypads, video out etc
- Apps and games can now use the iPod music
- Anti-Phising in Safari
- Safari can remember login credentials
- Calander now supports CalDav and .ics on top of mobileme and exchange
- Locate phone via a webpage & GPS (option in preffs)
- And the last thing I can think of is all apps can use bonjour bluetooth for a P2P network for connection to other iPhones/Touches for games etc.
Apple say that there are 100 new features and 1000 new APIs.