I used mine for a little over a year and never had any problems. I didn't get pg while using it, and I know my cycle so I know we were bd'ing while I was using it. It was very comfortable--i couldn't feel it once it was inserted, and you leave it in for a while afterward so I could sleep in it and take it out the next morning.
It was great...I'll go back to it for contraception after we (hopefully!) have this kid we are trying for!
Mom to Liz (14) and Dillon (3) and Mitchell FINALLY born 7/11/10!