Depends what kind of opinions. In the past I've had both kinds. The first, when your friends don't really 'get' the guy, don't find him attractive, think he's a bit weird, etc. In that case I'd shrug it off and go out with him if I really liked him. The second, when they are genuinely worried that he might not be the best thing for you, I listen to. However, your friends will not always be right, so if its the second type of opinion I'd advise a compromise - go out with him, but keep their warning in mind or something. Hope that helped.