I've actually found hahlo.com to work quite well. It's a web app that runs in the browser but it has a bunch of settings and such that work well with the PlayBook.
I saw twitter app Blaq on the playbook this week. Unfortunately the RiM rep would not provide me with a link for download. It still has bugs but hopefully a release real soon. I don't see Blaq on twitter much so hopefully they are putting a good app together. It shows previews of youtube links and you can play within the Blaq application. It reminds me of tweetdeck. Which is a good thing.
Honestly, I find tweeter's ability to accept tweets via email extremely handy when bridging and using my playbook. I can tweet from anywhere using my blackberry's already great e-mail client and without needing wifi.
