MooreBonds
Thinks s/he gets paid by the post
After I've booked economy class tickets on United, they frequently offer me the chance to buy up to business/first class. For a 3 hour domestic flight they usually want $300 for the round-trip. Which seems kind of steep, although if you were planning on buying "economy plus" (+$100) and checking a bag (+$50) then the incremental cost to get to first is only $150. Still more than I want to spend on a 3 hour flight. I think at +4 hours, the $300 upgrade would be worth it. But of course they want more than $300 for those longer flights.
I'm in the camp that would almost never pay for it.
Granted, IF I were flying on an airline that charged for checking a bag, and it were a long flight (10+ hours), I MIGHT consider it - but for most international flights, they'd want probably $1,000+++ for upgrading. And most int'l flights give you at least 1 or 2 checked bags for free.
I realize some people need leg room because of their height, but when I think about it, I just imagine taking a nice 7 day cruise with that pile of money they want to charge me, and think "Would I rather sit in a seat with more legroom for just a few hours and maybe get an alcoholic drink or two, and some crappy meal....or, spend an entire week on a cruise ship with some activities for the same money?".