Normally I build niche sites, and while they're usually successful, I also find the work quite tedious and not exactly challenging. The results make it well worth the effort though, and I'm earning a decent buck for the hours I put in. The part I enjoy the least about making sites is probably building links, and I'm sure many feel the same way. Sure, I could outsource, but I'm just too much of a control freak for that.
Anyway, like I said, my true passion in IM is testing and tracking, working to increase conversions. I also really like writing sales letters (I might not be an expert, but it's fun anyway).
So, what's YOUR true passion in IM (if you have one)? Is your passion also what you earn most of your income from? Is there something you absolutely hate doing?