Blazers bad luck dates, at least, from the Bill Walton "career-ending" injuries. After that, Sam Bowie. Then, they built a great team but weak inside. They drafted Petrovic and they sent him away to New Jersey. They drafted Sabonis but only could get him to play when he was playing on one leg. After that, they digged their own grave by signing Carlesimo... there was bad management, they throwed away the advantage of having Paul Allen and his big pockets, then the Jail Blazers... things seemed to work out better with Kevin Pritchard, they've drafted very well, but like mgent says, they gambled hard on injury prone players... and bad luck made the rest.
I think only the Clippers have a "bad luck" history in the same neighbourhood, but they have the worst owner in the league, so you can't compare both teams.
I've always liked the Blazers since they played against the Pistons, and was rooting for them when they faced MJ and Da Bulls. Adelman was a frustrating coach back then, but after those years he's made great great things.
And about rooting for other teams, I root for every team playing the Lakers, and back in the days, Da Bulls and the Bad Boys. In the 1988 and 1989 finals I wanted both teams to loose, but I hate the Lakers a lot more... Right now, I only root for the Celtics, although I like the OKC Zombies and the Mavs, and every team that makes the Fakers miserable.