In Google Reader, I select the entry I want to twitter and then hit Shift+T. Treader pops up a prompt pre-filled with the entry name and link.
I just edit the twitter to my liking, and hit OK. Treader posts it in the background using Twitter's API. I never have to leave Google Reader.
To try it for yourself:
- Install Greasemonkey if you haven't already. Greasemonkey requires Firefox.
- Install Treader.
- Reload Google Reader, select an entry you want to share, and then hit Shift+T. It will ask you to log into Twitter the first time through.
Thanks to Mihai for helping me work out the kinks.