Much to my surprise, it was super easy and everything worked perfectly! I used the triangle fold because it was the smallest I could remember without returning to my computer to look up different kinds, and got a decent seal the first time. No serious leakage yet, and when I went to empty and reinsert a couple of hours ago I was finally able to spin it! I can still feel it, but no more than I could feel a tampon during my entire cycle, and it's not even in a painful way. Removal is a little painful, but I'm starting to get the hang of it already so I'm pretty confident that I'll have it figured out in the next couple of days. I'm so excited, I can already tell that this is going to make things so much easier. I'm already trying to decide what brand I want to try next, lol.
So. :) Just another happy happy success story. Anyone lurking in the comm who hasn't bought a cup yet and is debating on getting one... do it! This might just be the best decision I've ever made.