Script Summary: Share and reblog to your tumblr from your google reader.
Install this script and visit your google reader, Share-on-Tumblr button or Reblog button appears on the bottom of each feeded article.
Click the button or press Shift+T, an input form pops up. And you can post about the article to your tumblr.
For reblog junkies: Press Shift+R, you can reblog without the form.