Ok Devs...  Sticky, sticky, sticky please, please please.

Oh, and Booster Packs, Booster Packs, Booster Packs, pretty please.

A suggested addition that seem to trip people up a lot:

Can an ally's activated powers be used on the opponents first turn after I play the ally?

No.  Allies cannot attack or use activated powers until they have been in play at the start of your turn.  That means an ally brought into play at the end of your turn by a card such as spirit healer will not be able to use activated powers on the opponents next turn.  However, payment powers (no exhaust required) can be used at any time after the ally is played. 

1120360:

However, payment powers (no exhaust required) can be used at any time after the ally is played. 

1125041:

1120360:

However, payment powers (no exhaust required) can be used at any time after the ally is played. 

I will point out (again) that it isn't an exhaustion cost per se that makes a payment power an activated power. An activated power has the activation icon as a cost. If power's cost is "exhaust foo," it's not an activated power.

Some payment powers have an activate symbol (exhaust symbol) as part of their cost. To pay that cost, exhaus the card that the power is on. These powers are called activated powers.

1125041:

So, by definition, an activated power is a payment power where exhausting is part of the cost.

Or did you mean that the symbol is technically the requirement, and a card that says in words "Exhaust [name]" would not be an activated power?

But for this very reason, we'll probably never see an ally that, through this loop-hole, can exhaust the turn it came into play. Most likely, cards will require you to exhaust 'target other ally' as the cost. Otherwise, if a card requires exhausting itself, we'll probably only ever see the exhaust symbol.

1125041:

1125041:

So, by definition, an activated power is a payment power where exhausting is part of the cost.

Take a closer look at the passage you cited. It's not exhausting as a cost that makes a payment power an activated power. It's the activate symbol. The cost for the power is not "exhaust," but "activate." To pay that cost, however, you do exhaust the ally. Look also at the glossary entry for "activate," which says quite plainly that "activate" itself is the cost. It's a subtle distinction, I admit.

Or did you mean that the symbol is technically the requirement, and a card that says in words "Exhaust [name]" would not be an activated power?

That's exactly what I mean. The cost has to be expressed as a symbol, not as the word "exhaust." I keep seeing people writing things like "because one of the costs is exhausting the ally, it's an activated power." That's not the case.

But for this very reason, we'll probably never see an ally that, through this loop-hole, can exhaust the turn it came into play. Most likely, cards will require you to exhaust 'target other ally' as the cost. Otherwise, if a card requires exhausting itself, we'll probably only ever see the exhaust symbol.

I'm not willing to speculate on what we will or won't see in the future. The distinction is there for the developers to use or not as they see fit, just as there's a difference between the syntax used for quests and payment powers (even though they're mechanically identical) that might some day be exploited. However, we've already seen an ally whose chief utility comes from a power that requires him to exhaust on the turn he comes into play: Tristan Rapidstrike. To be sure, his protector power isn't a payment power, so you may well be right.

You can attack with an ally or use its activate powers only if it has been in your party since the start of your turn

1126939:

So from my understanding if I recruit Dudefella on 4, I will have 1 resource left over to use his power during my opponents turn. It would seem a waste to have to go: End of my turn > Opponenents Turn > My Turn > Opponenents Turn before I can really use his power.

Unfortunately yes. To get the maximum effect out of Dudefella, you will have to wait that long.