Pheace: They only really matched Steam's Xmas sales I think so I doubt they lost much there since Steam users will stay with Steam on that.
January will probably be less active due to the good Amazon sale but most sales happened December anyway no doubt.
SimonG: I spent at least half the "christmas sale money" on Amazon, mostly the "big titles". Steam was the next big share, but mostly small games and bundles. The rest was GG,etc. (GOG was on hold due to CDPs legal shennanigans).
All the games I bought on Amazon were games I would have purchased otherwise on Steam. And I don't think I was the only one in that regard.
Overall I still think it will not have had such a huge impact, because mostly it was US only, unless you're one of the savvy who uses a fake billing address and the like, but that's not your average consumer.
That said, competition is always nice :)
klaattu: Steam Daily deal Flotilla -75%
Sweet, I've been wanting to get this for quite a while but it didn't want to dip under 50%, yay! :D
Kabuto: Duke Nukem Forever and DLC 75% Midweek Madness on steam
Duke Forever: $4.99
Duke Parody: $2.49
Duke Doctor Cloned me: $2.50
If you can find a Duke Nukem Forever -50% Coupon the game will be $2.49