Currently, the crop tool doesn't support the "keep aspect ratio" option out of the box. We will add it to our to-do list, but I can not give you a time frame.
If this is an important feature to you, the source code is available along with the rest of the controls. In it, you can see how the crop tool is implemented and make your own custom one by implementing the ITool interface.
As for the documentation - we are currently working to make it available as soon as possible. Until that is done, however, you can take a look at one of our latest blog posts
We'll be glad to answer any questions.
the Telerik team
Register for the Q2 2011 What's New Webinar Week. Mark your calendar for the week starting July 18th and book your seat for a walk through of all the exciting stuff we will ship with the new release!