I used the virtual river exercise in a college Introductory Physical Geology lab. The exercise has students measure the velocity and discharge of a virtual river. Students must do some calculations and must enter the correct answer before they can go on to the next page. It is an excellent exercise in which students collect and interprete data and learn about river dynamics at the same time. When students successfully complete the exercise, they print out a certificate of completion (which can be handed in to demonstrate that they have completed it). It took a little more than an hour for most of the students to finish the exercise. One slight drawback is that you can't go back in the exercise (eg to check some earlier data). If you stop for some reason, you have to start all over again. I found that the students generally enjoyed the exercise. but for some it became a bit of a competition. Some tried to get through the exercise as fast as possible without really thinking about what they were doing. In this regard it would be helpful to have a page at the end of the exercise which reviewed and quizzed the students the important concepts. Of course, this could be accomplished with a writing assignment for the class upon completion of the exercise. This is one of the best virtual geology lab exercises I've seen. I highly recommend it.