It's really easy to use and draw shapes even using a mouse. You can embed images from anywhere on the web into multiple pages. When you've finished creating your whiteboard pages you can download them, share them publicly online or email them to students (great way to send your students notes or their lesson).
You can use the software without registering, but if you want to save and share whiteboard flipcharts them you'll need to create a simple account (which doesn't seem to require any personal information beyond your email address).
- You can see a good tour showing you all the features here.
At present the public library of flipcharts isn't too impressive and just looks like people testing out the software, but if this takes off there could be a pretty impressive collection of teaching resources there.
If you can use this with a data projector and Camspace controller software, then you've got yourself a pretty cheap interactive whitebaord to use in class.