In general, when the IUD is installed correctly, the body does not perceive it as a foreign object or try to reject it or move about and puncture holes or increase the levels of copper in the blood or [insert another myth that seems to make intuitive sense but has no scientific or observed basis].
(There is one myth that has near truth to it. The common misconception that you have to have been pregnant to get it. This is not true either - the uterus just has to be big enough to house the IUD comfortably and and it's virtually guaranteed that a post-pregnancy uterus is. However for most pre-pregnancy women this not a problem either, and a size check is the first step during the installation process).
The benefits on the other hand are real, and huge. Reduced risk of hormone-associated cancers, noticeably increased sex-drive, better hair, nails, and skin, not having to take a pill every day, less money, statistically better protection from pregnancy, the list goes on.
My partner and I use Implanon, which has no associated cancer or heart risk. See my post: http://news.ycombinator.com/item?id=3774010
It's not perfect, but the side-effects are small and it's the most effective form of birth control besides true abstinence (as opposed to "virginity pledges," et al). Works for three years, nothing to remember, no risk of uterine perforation like IUDs, and none of the nasty estrogen side-effects.
Most issues with hormones is that they do all sort of stuff on yourbody. not only one controlled thing
Side effects of Oestrogen-containing contraceptives that don't seem to be caused by Progestin-only contraceptives include:
Increased risk of cancer
Increased risk of heart disease
Bone density reduction
Blood clots / Stroke
Increased sensitivity to UV (and associated skin cancers)
Reduced breast-milk production. This isn't very detrimental to one's own health, but does effect the health of the child.
The only down-side of Progestin-only pills versus Oestrogen-containing pills is that it is extra important that it be taken at the same time every day for full efficacy. Obviously the implant doesn't suffer from this drawback.
also, i have a paranoia that no hormone/protein/enzyme does less then a few things in your body. if they list only one or two effects, it's because they have no clue what else they do.
prolactin was believed to only affect the milk production in mamals for a long time (and water-salt control in fishes). now there's some other dozen effects on the body including neuron fiber formation.
No silver bullet.