My students ask me this everyday. They absolutely love it. I have mainly been using if for language and math. I found some great lessons in language on complete sentences and nouns and verbs. I have found that my students really understand the concept and their writing has improved.
I try to find a lesson everyday that goes along with what I am teaching in math. There are great lessons on estimation, rounding, greater than/less than, odd and even, fact families and more. All of these are in our GLETS and the kids have so much fun. They are all participating and paying attention when we use the Smartboard!