Helvetireader was a hosted user stylesheet for Google Reader served via a user-script. It aimed to make the interface a clean, minimal experience where you're not assaulted by an array of colours, social features and buttons. It was designed for people who just read the latest entries in expanded view without all the other gubbins.
It will probably break, but if you still want to try:
Install as a userscript for Firefox with Greasemonkey, Google Chrome (installs as an extension) or any Webkit browser (Safari, Omniweb etc.) with GreaseKit installed. For Opera, download the userscript to your user javascript folder.