Microsoft has been rolling out the SkyDrive Web Apps beta since about 2 weeks ago, but the feature seems now to have gone live to all users.
Now Office Documents when clicked on are opened in the new, more sophisticated web apps, such the OneNote app above.
Users are also able to create Word, Excel, PowerPoint and OneNote documents from scratch, meaning if your needs a very undemanding you will not need to pay for Office at all.
The feature can be found by visiting your SkyDrive storage.
Thanks Ludwig for the tip.