If I did not read outside my comfort zone, I would no doubt be stuck reading Forgotten Realms books and avoiding anything written in the first person perspective. I have always envisioned reading as a journey, from where I began, to the small steps I took away from there, to where I might go in the future. I like change and I don't like to settle on any one type of book for too long--I can't even stomach reading a the books in series back to back. That means that I frequently step outside my comfort zone. My experiences have been largely positive... except for YA. I have attempted a few, which range from the highly praised (Scott Westerfeld's Leviathan) to authored by one of my favorite authors (Carlos Ruiz Zafon's Prince of Mist) and the experiences have either been mediocre or just plain bad (the latter falls into this category, unfortunately).
A large part of not having many negative experiences is knowing where not to tread. There aren't many sections I won't step into, but I am not going to browse the Romance section or pick up an Erotica novel (though I've sampled a few over my fiancée's shoulder and cracked up over how bad they are written, which she'll admit to, even if she has a shelf full and can't resist buying more). There are things I haven't tried, many things, and I am sure I will run into negative experiences in the future... and, of course, there will be things I avoid (for instance, unlike RSAShark, I am uninterested in sports and avoid books concerning them like a plague).
There is a downside to expanding your reading horizons though. There are many more books vying for your hard earned money and taking up shelf/table/desk/counter/floor/couch/chair space.