Since Dr Oz mention using green coffee bean extract for weight loss, there has been a huge amount of interest on the topic! While early studies show the chlorogenic acid in green coffee beans may have health advantages, more studies are needed.
So far- from the few reliable studies and updates I've seen, there are no serious side effects from green coffee for otherwise healthy individuals.
Green coffee beans DO contain CAFFIENE so anyone who has issues with insomnia, irritability, stomache upsets and so on from caffiene may wish to avoid using green coffee bean products.
On a personal note: I have a friend who has been using coffee bean supplements for a wjhile and she reports improved energy, focus, and general well-being without the jitters and insomnia she has with regular coffee.