I just usually figure when someone makes a statement of something they think is "the best" or such, that it IS their opinion.
I don't have a problem with it, as I say this also, but it does seem superfluous... but it's part of our culture and language. We tend to feel like a statement of our opinions are naked without it.
I've said(written this) many times only to have my opinion challenged anyway, to which I have to point out that I already said IMO(I don't believe I ever used IMHO)
I think we do this to try to avoid having to get in a debate, but some people want to argue so much that this phrase doesn't even register.
Of course this is just my opinion, lol!