My Eberron game is up to 17th level now and I can say if you design a character to use AP and take the feats to enhance them they can be pretty powerful. If you don't, they are just a minor boost now and then.
What I am wondering is how many DMs assign APs to the NPCs too? I give NPC groups a pool of AP (3 or so) per encounter. The NPCs as a group can expend no more than 1 per round and only 1 gains the benefit (usually the leader). They must be an actual group (not a collection of individuals), acting in some sort of high-action situation like combat. The NPCs also regain a point for their pool each round any PC uses one to a maximum pool size of 3.
Certain class like the Marshal (MiniHB) allow more than 1 NPC to draw a point from the pool in the same round so long as they are under the Marshal's direct command and they grant other enhanced AP benefits to those under their command.This allows weaker and generally less-equipped NPCs to generate an occasional threat to the PCs now and then without massively increasing their power.
Of course, major NPCs can have the Heroic Surge feat (or whatever it's called) and they account for AP under those rules not my NPC group pool rules.
Tzarevitch