Virtual Manipulatives

I really enjoyed using virtual manipulatives at school and it was a great way to reinforce rules of geometry. Once I got the hang of the game, it was fun and  I wanted to keep playing, even when class ended. I realized how educational this could be in my placement where we teach fifth grade math and we just finished a unit on geometric shapes and rules.
We use "Envision" math curriculum and it has many similar games for students to play to learn and reinforce math concepts. We have not played them in class before until yesterday and I have never seen so many hands raised at once for students to come up to the board and show what they know!  It was unbelievable! They could not contain themselves and were out of their seats hoping to be the next one called on, they were talking over each other, etc. They loved it and it was obvious that many of the students play these games at home and I'll bet the rest will be from now on. They were even fighting over who got to go up to the board and show each other how to log on to the website!
Applications for virtual manipulatives in the classroom are endless. When I saw how excited students were to use them, I immediatly thought about how they could help with classroom management. They provide a great incentive for getting students to stay on task and do their work during class time. Teachers could give students a chance to use the computer at the end of class or the end of the week or something like that when they finish their work.
I wonder how, logistically, using math games as incentives for desired behavior could be managed well. I will ponder this and try it out next quarter. I see problems if  only some students (e.g. who were done with their work) got to play the games while others still had to finish work, particularly with the noise level and the distractions created by the players.