While the update is indeed rolling out OTA, there is a way to install the update right now if you so wish. If you do Menu > Settings > About Phone > System Update you should be prompted to update your Defy.
The update is 112MB so it might take some time to install after you receive notification as well. For those interested, here are just some of the things included with the Froyo update for the Motorola Defy:
Adobe Flash Player 10.1 Support: Performance of the phone has been enhanced resulting in faster user interface, application operation, and Web browsing.
Better overall phone speed and performance: Your device now supports Adobe® Flash® Player 10.1, allowing access to rich Web content and games. Adobe Flash Player 10.1 is installed along with this upgrade.
App storage and updating: Applications can now be stored on the device’s microSD card. Additionally, apps can be set to automatically update by checking “allow automatic updating” under each app’s page in Android Market™.
Wi-Fi Hotspot: Phone can provide an Internet connection for up to 5 Wi-Fi-enabled devices
Digital Keyboard: Added punctuation to the suggestion ribbon.
A full list of enhancements can be found here. Enjoy your scoop of Froyo Defy owners and keep your fingers crossed that you’ll see Gingerbread at some point as well.