Ummm... I may be wrong, but as I understand it (As it was explained by my doctor) the IUD doesn't affect your milk supply / breastfeeding, and the chances of it moving are very slim - but they teach you to feel the strings that hang down out of the cervix and into the vagina so you can tell if it's no longer in place and get it sorted out asap hopefully before infection can set in - there is that risk of course, but it really is minimal.
If you want to avoid the pill because you're breastfeeding / don't trust yourself to remember to take it (or for whatever reason) and you don't like condoms, then the IUD is a good option for some because it is over 99% effective, has very few side effects and is reasonably long-term (can be used for over 5 years without needing to change it or use another form of contraception) but your fertility returns to normal as soon as the device is removed...
I don't have any first hand experience, though - just the facts handed to me on an information booklet
