Are you worried about Iran's nuclear developments?

Recently Iran got its nuclear power plant up and running, and within the year has claimed they will have refined enough uranium to fuel the station. Refined uranium can, of course, be used for nuclear weapons if it is at the weapons-grade level. This level is far more refined than that required for the plant.

Are people concerned about nuclear proliferation in Iran? Are there any good sources to recommend to keep up on the issue? What do you think is the appropriate response from the United States or the International Community?