It won't surprise you to hear that some Chrome extensions behave badly, but how do you spot malicious activity when it isn't always obvious? Google might soon have a way. Techdows has noticed a recent code submission for an "activity log stream" that would show extension tasks as they happen, with the option to freeze things if you spot something unusual. You'd likely need some technical knowledge to make sense of the data, but this could help you catch add-ons that siphon your data or otherwise go rogue without telltale signs.
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.