It's a pretty nasty bug. To quote from the above advisory:
The impacts of this vulnerability include:
* Read-access to files on the victim's file system * Read-access to lists of files and folders on the victim's file system * Read-access to emails written or received by M2, Opera's mail program * Cookie theft * URL spoofing (phishing) * Track user browsing history * Much more...
This one's a very important download, folks. Get it while it's hot!