I used Poll Everywhere and think it could be a very fun and useful way to see how well my students understand the material. I could use this when reviewing for a test or when we do TAKS or STAAR test review. The students enjoy when they have an opportunity to text in class. It mixes things up and diversifies activities a little bit.
Here is a link to my poll: http://www.polleverywhere.com/multiple_choice_polls/MjA0ODI2Nzg0MQ
I also created a TodaysMeet. I like this better than Twitter for a classroom discussion because the students do not need an account. It is also very user friendly. In a classroom setting, I would require that the students post something appropriate that adds to the discussion. This could be really great for students who are afraid to share in a large group setting, but have many thoughts to share.
Here is the link to my TodaysMeet: http://todaysmeet.com/MathModelsNHS