The CIEE program in Prague is definitely worthwhile. I had a great time, and although I had some disappointments, the traveling experience, the culture shock, really helped me to understand there is more than just a US way of living. This is something I thought I already understood, but I was incorrect, and now I feel I have a better understanding of what is important in life.
I enjoyed my classes, although they didn't see quite as rigorous as my courses at home, The topics were unlike anything I could study at the University of Arkansas and kept me interested and my mind stimulated.
CIEE tried to do a lot of things for us in the beginning to get us out and seeing the country, but that soon waned and eventually stopped altogether. But I would hang out with friends (local and other CIEE students) on the weekends quite a bit, and classes only Mon-Thursday was really nice.
If you're keen to spend a semester in a non-traditional country (i.e. Italy or France), then studying in Prague definitely fits the bill and I can't recommend it enough. Have fun!