Personally, I loves me some AP.
I actually prefer an AP-centric game style, like Grim Tales, where Action Points are required to confirm critical hits and/or the GM can dole them out to confirm his own crits or activate critical fumbles.
Of course, for me, I like a bit more literary drama in my game, and it allows myself and the players a little more control over things ... they can decide not to confirm the crit on the mook with 2hp left anyway, or choose to confirm on the mook who they just hit and maybe get the one-shot-drop for "Woo Hoo" standing-up-at-the-table fun.
I too allow them to be used to emulate feats, which I haven't found to bog down the game. Usually it's a feat like Improved Initiative or Cleave or something in a feat chain they're building TOWARD but don't yet have. By making sure they have the prereqs, it cuts down on what's available and I don't let people go flipping through manuals looking for "The Perfect Feat For Right Now". IME, people usually use it for a feat they're going to actually take later ... sort of a Feat Test Drive.
I'm even in the process of drafting up a new house rule to add to APs ... not finished with it yet. Basically:
If you have a Racial or Feat bonus to a save or skill check, you can use an AP to "Get 20" on a check of that type once per (session?).
Either "Get 20" or "Reroll Check" ... not sure yet. At any rate, the reasoning behind it is to highlight the "racial identity" bits a little more heavily. Early levels, a +1 to hit Goblinoids might be okay, but by lvl12 you usually forget you have it. This lets you crank up the "Elfness" once in a while and say: "I did this because I'm an Elf and we (see secret doors) or (are resistant to Enchantments)." It also adds benefit to the +2-to-Save or +2-to-two-skills feats, by opening up a chance to say: "I have unusually Great Fortitude, thus I resisted that poison."
The flip side would be the GM could then give you an AP and force you to "take 1" or "reroll" a check on which you have a racial penalty AND open up role-playing-oriented "Disadvantages". A Disadvantage, then, would net you nothing up front ... but if you, say, took "Dimwitted, -1 to Knowledge checks" as a disad, it opens things up so that the GM can "award" you APs by activating your disadvantage and forcing you to reroll or fail thematic checks.
Still in the rough-cut stages.
--fje