Programatically-generated landing pages. Where are the limits?

We know that this is part and parcel of lots of operations. Surely there have to be limits in terms of when Google (and others) will take a look at these auto-magic pages and simply ignore them. Or, worst, trigger a site de-listing for being "spammy".

Any sense of where the limits might be?

Hypothetical example:

You are trying to get people to a site that gives you instant quotes on airplane flights within various cities in the US.

One could very easily write a piece of code that would spit out thousands of legal city combinations in the form pages named:

"price-to-fly-from-<city 1>-to-<city 2>.html"

Pepper each one with a few variations of a story and you have hundreds or thousands of pages to feed people into your sign-up form.

I am sure this doesn't work quite like that any more. Where are the limits? When does it become dangerous (de-listing).

Not trying to game the system at my end, just trying to understand how not to get into trouble by simply not being up to speed on what the search gods have deemed to be acceptable or not. Considering how totalitarian the approach can be it is prudent to seek feedback on this before launching a hundred landing pages only to end-up de-listed.