Never Gone was weird because they did that club tour months before it came out and sang some of the new songs, so we'd heard about half of them through that - Beautiful Woman, Poster Girl, Weird World, Climbing the Walls, Incomplete of course, and maybe I Still? I still think half of NG was new to me when it came out, though, and I don't remember going out of my way to avoid leaks - I pretty much watched and listened to everything during that era.
I know a few songs off Unbreakable leaked, and because of that, I know I avoided the leaks like the plague for TIU. The only song I'd heard when that came out was Straight Through My Heart.
They also had all those unreleased songs for Never Gone which I ended up loving as much if not even more than some of the ones that made the album.
Never Gone was my first real experience as a full fledged BSB fan. That little club tour was the first time I ever saw them in concert.
I listened to maybe one of the leaked songs from Unbreakable but then decided I wanted to be surprised. For This Is Us, I listened to one or two but then disliked them so much I was kind of afraid to listen to the rest.