Apparently, two extensions already exist: Google Mail Checker and BuildBot Monitor. Mail Checker keeps an eye on your Google Mail, displaying the number of messages in your inbox on the Google Chrome toolbar. BuildBot keeps track of the current status of the Chromium build, and notifies you when a newer build is available for download.
According to Siegler, installation is a breeze: “Installing these extensions is a breeze. You click the “Install” link, the file downloads, you click to run it, it asks if you’re sure you want to install the extension, you say “yes”, and you’re done. There is no need to restart Chrome/Chromium, they work right away.” Unlike Firefox it’s load and go. And Siegler reports that Chrome extensions don’t, yet, slow down the browser, like they do in Firefox.