You can try the feature now in the experimental Chrome Canary browser by enabling a flag (--enable-extension-activity-logging) and visiting the chrome://extensions page. You may have to wait a while before you can try this in a more reliable Chrome release, though. It's not clear when this will reach a beta, let alone the polished version. If it does carry over to finished releases, though, it could help both researchers and curious users identify malicious extensions -- not to mention discourage those who'd try to sneak hostile code into your browser.