CERF and Nettrekker

I have finally had a chance to explore CERF a bit and I have found it to be a very useful tool. I checked out their website to get some general info (http://www.cerfinfo.com/) which clearly explains what a great product it is. Just this week the kids at PV experimented with Nettrekker and they truly enjoyed it. I have had 3 teachers come up to me after their lesson and tell me how much the kids enjoyed it and how easy it was for students to use. Has anyone used CERF with their students? I would be curious to hear student reaction.