I've had the Diva Cup for 6 months and I LOVE it.
To the mama who said this "hit her gag reflex," I wanted to say...I understand. I was kind of shocked by the idea when I first read about it...but then I researched. And I bought one. I've found my Diva Cup to be 100 times less gross than tampons. There's nothing filling up my trash can or being flushed into the environment. And even toileting is far more enjoyable...since it all stays UP THERE.
Since using this product, I'll tell you...I'm more grossed out by tampons and pads than I ever was. A menstrual cup is extremely hygenic, safe, and actually a joy to use. I don't have to worry about getting TSS and I don't have to be dependent on getting to a restroom every 2-3 hours! This is especially fabulous for me as a Soldier.
ETA: Leah, there is no smell. And yes, you can use it with an IUD. Here's what the Diva Cup FAQ says (just search IUD): http://www.divacup.com/en/home/faqs/