I'm not overly enamoured with the backing tracks, but I don't hate them. I've voted "don't like" - I'd rather they just performed live, warts and all. I like the rough edges, I like the authenticity of live music, but as long as they're not miming to them and not trying to deceive the audience, I'm basically fine with it. No objections, but I'm not crazy about it either.
What I do slightly object to though, and I'm sorry about this KevShmev, but I hugely disagree with you invoking the intro tapes. "It's similar, so it's the same, and it's hypocritical to like one and not the other" is kind of a logical fallacy. I'm sure you're not trying to be duplicitous or devious or manufacture consent and that you were posting in good faith, but while they are similar inasmuch as both make use of pre-recorded backing tracks, it's to completely different effect. I really like the intro tapes - I like the dark stage, the mounting excitement, the huge wall of noise when the band takes over. There's an excitement to it, a showmanship - and that applies to Metropolis, ACOS and Pull Me Under where they played the music on the album just as much as it does to The Shaman's Trance where they didn't.
I'm not so hot on backing vocals because it's a level of perfectionism that I don't really look for in live music. What would be more comparable would be, as Blob suggested earlier, a tape of a guitar riff played during the song - during the Peruvian Skies solo, for instance. And there, I'm just as cold to pre-recorded backing vocals as I would be to pre-recorded music. It's not a double standard, it's different techniques.