My gyno said that breakthrough bleeding can happen once you've been on the same pill for a long time-- I guess your body kinda gets used to it, or something.
I use the Mirena and I love it... except for the breakthrough bleeding. It isn't enough for me to discontinue it, but it is a problem. I haven't had a real period though since I had it put in 15 months ago. It isn't totally hormone free (Paraguard, the copper IUD is, but many people have VERY heavy bleeding with it) but it is a very low dose of hormones that is thought to act locally, rather than systemically.
Having it placed was painful for me (for about 30 seconds, but WOW!), but I had never dilated (planned C- with my son). I suspect that if you had any of your kids vaginally, you would have less pain. Anyway, for 5 years, you won't have to think about birth control, which is the biggest plus!