My OB (who reads these forums) says that 70-90% of IUD users love it! Now, some of those may have symptoms that they aren't aware are IUD-related, but I wouldn't think many. He is aware of the common symptoms like hair loss, acne, cysts so he isn't lying like some do and would recognise them if a patient experienced them.
A group like this is going to have all the possible worst effects. If we didn't, would we read or post here? Or just go out and enjoy?
What I'd do is ask your OB what will happen if you have problems. And reading here, you know the common symptoms so if they happen to you, you will know why and can get it fixed right away and not suffer for a long time, not knowing it's the IUD, which is the thing that I think we generally hate most!