So I finally got my "set feed channel opacity relative to the unread count of that channel" script to work on Google Reader via XBL and the DOM, instead of relying on the names of functions and variables within google's code. The result being that the script should continue to work even after google makes changes to their code.

Installing it is not too hard, and is done thusly (I assume you're using firefox, although in theory any mozilla-based browser will work):

• Download this XML file to Firefox's resource folder. For mac, this is /Applications/Firefox.app/Contents/MacOS/res. For windows, this will be something like C:\Program Files\Mozilla Firefox\res.
  Linux users can hopefully figure out the eqivalent path, as I don't have a linux box handy.
   
• Add the following code to your userContent.css file (in your profile directory):

@-moz-document url-prefix("http://www.google.com/reader/view/"){ li.unread > a > span > span:last-child{ -moz-binding: url('resource:/res/greader_binding.xml#item_filter'); } }

Thanks to Mihai Parparita for pointing me in the right direction (I'd never heard of XBL before this...)