Google Chrome will eventually support add-ons and user scripts
You can install add-ons for web browsers like Firefox that do everything from turn the browser into an FTP client to provide email notifications. And there are user scripts that will let you change the way you interact with web pages. Google Chrome doesn't currently support either type of extensions. But it will.
At the Web 2.0 Expo in New York, Google's Ojan Vafai indicated that Chrome wll support both eventually. But first, the developers want to make sure that add-ons don't cause the browser to become unstable. Firefox add-ons, for example, can bog down the application, making it take longer to launch and more likely to crash.
While you're waiting for Google to figure things out, there are always workarounds that let you install user scripts or block ads in Chrome.