I have a Mirena IUD. I have always had mixed feelings about it. First of all, I never really read up on its safety. Sometimes I feel that it irritates DH and I. He has complained that he can feel it every now and then. From what I read on their website, I guess I can go in to the doctor and get the strings trimmed, but I'm thinking about having it removed soon so I can have another baby.
I do like that it is always there and has a very low failure rate.
I would go on their website and read the FAQs. It has some stuff about risks and benefits.