I had cleared Darklight Tower or whatever that place was and got Illia as a follower. She was by far my favorite! Took her everywhere. We were like peas and carrots.
Then I started the Companions quest line and when I had to take Farkas or whatever that dude's name was with me to Dustman's Carn, the game automatically dismissed Illia and I could never reacquire her companionship afterwards no matter how I tried. I think that was the instance that caused me to create an account and come here. Then as things got progressively worse, I stayed.