Many thanks to Alexander Atallah for pointing out how to get the gReader theme working in Safari 3 again.
Forget SafariStand, and go get yourself CreamMonkey, the Greasemonkey style plugin for Safari. Once installed, you will see a smiley in your menubar, then when you visit these 2 pages on userstyles:
OS X Style Google Reader
OS X Spinner for Google Reader
You will see a ‘Load as User Script’ button. Click this, and then ‘install’ when the sheet appears. You’ll then just need to refresh gReader.
It not only works in Safari 3, but it also only applies it to that URL, just like in Mozilla! So you shouldn’t be getting the style affecting other Google pages.