Hmm.. I don't actually like them, but I'll certainly tolerate them or perhaps even enjoy it if they're designed well and have a compelling lead-up behind them. I'm actually going to eventually go back over the crystal cave thing in my mod to make it feel like less of a fetch quest.
So, yeah. Avoid if possible, but try to give a good reason for it if you do make one. The problem with fetch quests is that they're one of those things that's been done to death in like, every game ever made, so it doesn't add much originality.