I TRY to read a number of spoiler free reviews leading up to a movie.
Occasionally I unintentionally stumble onto a spoilery review, or a self proclaimed "spoiler free" review just drops a bomb mid way, hence the "try", but usually I'm fairly good at avoiding them when I really want to.
While I DO form my own opinions of films, with ones that I am highly anticipating, I like to get a sense of whether or not the film will, potentially, let me down before I go in. As opposed to going in fully hyped, only to crash hard with the let down.
That's not to say I let the reviews define my expectations, but rather prepare me for certain possibilities.
I'd much rather go in hesitantly optimistic, and be gleefully surprised, than go in overly enthused, and end up thoroughly disappointed.