One huge change that has impacted me - both positively and negatively - is that airlines now actually try to sell their F/J seats to individual buyers on many routes.

In the 90's, it was almost exclusively corporate buyers + upgraders. Airlines would price the seats astronomically high and then give corp discounts of 40-50% if not more. (I know some of my J tickets for work in the 90's, ex-ORD on AA, were 45% off list price.) Since the corporate travel didn't fill every seat, and you could kind of predict when it wouldn't fill the seats, the upgrade game was quite a bit better.

Now, airlines have realized that individuals will buy the seats and pay a profitable premium for them. They can use a few simple fare rules (advance purchase, nonrefundable, etc.) to firewall the individuals from the corporate buyers and collect a lot of revenue from the seats without cannibalizing the full-J sales.

The positive angle, for me, is that now I've actually bought a few J and F tickets for leisure trips. Trips where the total F/J airfare is equal to the cheapest coach seat + an "upgrade fee" I find reasonable for the product. The negative angle, of course, is that awards are often a lot harder to find...