Ever since Steam did it, I only bought 1 game from them (Zeno Clash) and it was because it was a 24-hour insane discount. Yes, I was weak but no more! I'll never buy another game from Steam again, and no Christmas sale will change my mind.
So yeah, if GOG ever did something like that, I'd set fire to an orphanage to express my rage. What about you?

Some dethklok style blacker than the blackest black times infinity expression of pain and rage that causes the deaths of those that love me most
Well that or send them an articulate expression of disappointment outlining the way that it would do more harm than good to their business structure and cost them the immense reserve of consumer good will they've built up.
Depends on my mood at the time

I'd do what I'm doing with Steam : scarcely buying things from them

Rant on twitter? Only buy games that are on equal worldwide pricing? Or If I feel like breaking form, also buying those where Australia is the cheapest?
Worldwide price gouging is not something in itself that would stop me using this service, but for me, it is a big mark against anyone that does it.
Can't see them going this way unless they get taken over by MegaEvilCorp5000. Goodwill, trust and so forth is fairly high here compared to a few other DD services.

I doubt they'd sell to activision...

Wouldn't give a shit. Hell, the DRMless games and extras are worth any amount of money IMO.

Never gonna happen, so the point is kinda moot, but if it did, it probably wouldn't affect me in the least, since it seems most of these regional pricing scams actually come out in favor of US customers.

Let's see, I'd decide if the games being offered were worth the prices in being asked in my region, then buy or not buy according. Pretty much the same as I do now. I suppose I'm just a rather pragmatic person.

probably only buy Games during Specials and use GoG Codes if i was lucky enough to get one.

I send the money to a US buddy and he gifts it to me. Or I use my region free debit card + canadian IP and gift it to me. Both circumvent the problem entirely.
Though I agree it is a rather shameful move on Valves part. Its always the customer who gets boned by some idiots in suits who decide to do stuff for no real reason. :(

Capitalism and the New World Order! Such a beautiful thing. /sarcasm
I don't know if GOG would do such a thing as they are European based, actually care about their customers, and are awesome people made of gold, fairy dust and other good things.
Since I don't live in Europe, it probably wouldn't affect me financially.. But respect would go out the window, definitely.

i would sign an online petition.

this, and i'd raise hell on the forums. HELL I TELL YUO!

Depends how reasonable the pricing is, but there should be no reason to increase prices for Europe if we are paying the US $ equivalent. It should be a level playing-field worldwide.
If it's forced by taxes being levied on top of European payments or something, I'd be happy to pay a little extra, but otherwise I'd be very unhappy.
I've stopped buying Steam games, and I'd have no difficulty in doing the same for other stores, as well as making my feelings plain on the subject.

This would only hurt GOG not me as I would be buying far fewer games.