I used a paraguard IUD for 2 years. It did cause heavier periods, but for me that was a small price to pay to have easy, nonhormonal birth control. When I had it put in, my doctor told me to check every month after my period to make sure it was still in place correctly. I did that at first, but not consistently later on. I should have. About two years after having it put in, and about 2 weeks after my period should have started, I checked and discovered that it was much lower than it should have been. I took a pregnancy test, which confirmed my fears. My doctor said this was a rare occurence, but not unheard of.
So I guess the main point is, it is an easy and effective form of birth control when used correctly. Just don't get lazy about checking to make sure it stays where it is supposed to be.