I had no problems. No one at my school has ever had any problems and we're talking 100s of students here.
one of my friends has waited 6 months for his J1 visa, and he still waiting!!!!
Any problems I have ever heard of are induced by sponsoring organisation or you not having the correct paperwork in order.
Follow the instructions - don't interpret them! If you follow them you will have no problems. They are more than comprehensive enough - to cover nearly all of your questions.