ohh god! my neighbor wont give me back my mw2 game, this is just gonna make everything worse when i see him.

Is this for all systems?

Yep. From everything I've looked up (it's never stated anywhere) it seems to be on all three systems, include the PC

I wondered why I was getting double xp earlier.

Yeah my brother was wondering as well and gave me a call. He's like "Is it double xp weekend?" I'm like: "Uhhh...I don't know, give me a second" and voila..it is (I remember being told earlier on in the week or seeing something about it earlier but I missed Bowling's tweet that it went live. That's the one problem about trying to follow a lot of people..you get lost

Oh sweet, I'm just 8 levels away from my 7th prestige so this should make it that much easier.

I never noticed, but does double xp affect challenges too?

Like say I get 300 kills with a gun, does it give me 20k instead of 10k?

Negative, just gives you double XP and that's it. Would be nice if it counted twice (kills and stuff)

Its simply way too annoying playing against prestige 10 players and their 10 classes. I just hacked my way to prestige 9, but rank 1 and started unlocking everything from there, so just have to do it once. I chose prestige 9 because there is no difference between 9 & 10 other than the badge and people don't suspect you've hacked since they don't know the 9 badge.

im playing modern warfare 2 and im not getting any xp points on playstation 3

This was from September 2010 so you're a year late unfortunately.

It's a double XP weekend on the 360 this weekend. Not sure about PS3.

Should be on all platforms this time (it's not tied to a map pack release) and I believe I heard JD clarifying it being on all platforms in a recent tweet

I am pretty sure it is on ps3, i was getting +100 every kill, and i am sure it is normally 50.

Isn't it 100 points a kill in mw2?

Kill points are dependent on game mode in all CoD titles.