I was just idly wondering about bookmarklet functionality for Drupal. I found this, which I think is based on Julian Bond's earlier work.
Here's the code -- replace www.bryght.com with the URL of your own Drupal install to get it working for you. As well, you'll need to remove the line-breaks.
javascript:t=window.getSelection();
void(window.open('http://www.bryght.com/node/add/blog?edit[title]='+escape(document.title)
+'&edit[body]='+escape(t)+'','_blank',
'width=710,height=500,status=yes,resizable=yes,scrollbars=yes'));
(same code as a link - drag to your bookmarks bar to install)
Of course, you do need to be logged in to your site in order for this to work, and it's set to create a blog node automatically (weblink might also be good). I think this is a good feature for regular users, so I'm going to do some more thinking about this. I put up a wiki page that you can edit if you like.