Anyway... there's already a ton of posts, but I only read the first page, so tell me if I'm repeating anyone.
Opinions are just beliefs about the world, which are often subjective and rather vague when presented as opinions. You can't say any one is wrong, exactly, but an opinion is pointless and flaccid without justification. I other words, there still has to be reason behind an opinion; obviously, a rational person shouldn't hold a poorly justified opinion. "I hated that movie" is an opinion, and I suppose it can't be "proven wrong," as you might disprove a geocentric universe or w/e, but unless you unless you add "The size of the lead's head distracted me the whole time," you're just talking out of your ass.
People fly the "IMO" banner so they don't have to justify themselves; like going "IMO, there shouldn't be a mosque near ground zero." That's stupid though. The fact that it's "your opinion" doesn't justify the statement. It's irresponsible to assert conclusions without support, especially if you continue to ignore others who try to convince you otherwise (perhaps by trowing down a lot of facts) by saying things like "yeah, that's great, but it's just my opinion." That is when you're "wrong" about your opinion.
On another note, I don't think opinion and facts are necessarily opposite, based on how I've heard the terms used in college. I'll leave it at that for now.