Firstly check out the rules HERE (on page 12). How do you think would work in 4e? Personally, I love it, as it means that nastier abilities (or ones that only trigger under certain circumstances) can be harder to shift, without the players having to keep track of numerous save modifiers (beyond those of their own attacks and items).
In my games we have stopped using XP, instead going for a more story based system (i.e. the characters go up a level when it seems right). This has lead to me giving out more action points as rewards for battles well fought, and for particularly good examples of players sticking to their characters - even if it isn't the best idea for them...or occasionally, their group. With this in mind, Dave (of Veteran and Jaeger fame), suggested allowing players to spend an action point to reduce a save to the next lowest category....
I like this a lot, as it add another use to the growing array of action point abilities (if you wonder what I am talking about, check out "Combat Options" in Dragon 425), and it forces the players to make some tough decisions.
Anyway, I intend to start making use of the 13th Age style saves, and will let you know how it all goes!