Don't say it every other second, it sounds insincere. But I agree, hearing it every so often from the right person is a wonderful thing.
Everyone's insecure about their looks at some point, I think.
And I think this point is valid for men too. A story: I have this male friend who is absolutely, absolutely gorgeous. Every female friend I've introduced him to has gotten an instant crush on him once they meet. (Nothing's ever happened between us...he's like an older brother to me.) A few years ago I was visiting him and we went out to this club. There was this girl there who he'd seen several times before but hadn't the guts to go up and talk to. One of his friends sent this girl a drink from him right before we all left...well, he was freaking out about that, saying that he can't go up and talk to her now because his friend did that. That he didn't think she would want him to talk to her...blah blah blah. I swear it sounded like the kind of conversations some of my female friends and I had about guys! (He's married now, by the way.)