I hope Michael isn't the only secret but I'm pretty sure he won't be, what is it important to me though is that the Michael twist doesn't end early like the rest of their sh*tty little twists. It's the main 'secret', the one that was promoted for weeks and for them to end it at the end of this week or something before it's even got going will be utterly pointless. This is the one opportunity they have to do this twist properly and they need to do it right and let him settle down next week and stop shoving him in the housemates faces to make it obvious, I want him to turn nasty and start being more devious, he should be forming close bonds with people only to tear them apart 10 weeks down the line when they find out he's an actor
Also, contrast their reaction in a few days if they reveal it to him (they won't be surprised), to if he actually settles in and becomes part of the group normally and then at the end of the series they reveal everything they thought they knew about him and all the stuff he's done has been part of an act...now that'd be miles better.
It doesn't mean he takes over the series (he hasn't taken over the highlights yet), you can have him doing a couple of viewer decisions a week and still have other house action. And then throughout the series there can be loads of other twists too, like a secret house, maybe bringing another housemate in on the Michael thing, turning another one of them into an actor...revealing one of them is actually an actor too (why do I get the feeling this could happen).
But yeah, the Michael thing is the main twist they promoted and it needs to stay the length, otherwise I am going to be so pissed off.