Google adds Gmail's 'suspicious activity' monitoring to your Google Dashboard
It's very cool, and it works really well. I have multiple friends that have caught hackers (usually from China!) just moments after they've gained access to their private email accounts. With Dashboard now enabled -- and thus every single Google-owned website -- you will have unprecedented security from identity theft attempts,World of Warcraft password stealing, generic hack attempts... and so on!
The only problem is that you need to visit the Google Dashboard to receive the warnings. You won't get a warning by simply browsing YouTube or Picassa -- you'll only see the 'suspicious activity' dialog box if you visit the Dashboard (or Gmail).
Still, it's better than nothing! You should check your Dashboard and marvel at just how much information you've given Google too...