The new fire fast mentality being pushed is not for performance though. It is you are a rockstar at X, but now we need X+1, you're fired. Basically companies are starting to treat full time employees as contract employees without paying the increased contract rates.

Exactly my point, and I'm ok with that if they're up front about it and they give me some lead time on when X+1 is happening.

Personally I'd prefer a place where I could do X and X+1 so it'd be a bit of a negative in choosing where to go, but I can live with it. OTOH I'd be extremely pissed if I walked in one day and was told "we think you're awesome, but you don't konw X+1 so see ya later"

The problem is, these companies are being run by people who can't tell the difference between X and X/10, let alone X and X+1.

But they think they can because they got VC money and they are high on their own fumes.

Fire fast if someone is clearly not a right fit, but "Fast" should be after giving them plenty of warning.

Absolutely agree, it's just that it doesn't always happen. I tell every new boss that I'll be completely upfront w/ them regarding my thoughts on how things are going, if I'm thinking of jumping ship, etc - but in return I expect them to do the same.

Ideally both sides are on the same page at any point of time as to what the situation is.

Wow. I would never say I was going to jump ship until I had my plans set out. In the past I've given 6 weeks notice when it was asked for but I just wouldn't put myself in a situation where they might fire me before I fund my next gig.

There's a difference between saying "I'm jumping ship" and "I'm thinking about looking around in the next few months". The former is implying it's definitely going to happen, the latter is saying that it's a fungible situation.

I'd like to think (and try to only work for) people would be professional enough on both sides to realize that not everyone (either side) is going to be happy 100% of the time but a) both sides can work on it to make it better and b) if it doesn't work out, try to be supportive of each other so that both come out stronger overall.

It still sounds sketchy to me. Threatening to leave is giving your employer an ultimatum. Personally, I think the rational response to this is to placate you, find your replacement, then fire you. If you actually have issues with your work environment, you should address those head on without the threat of leaving the company.