Good question. I think xp from kills goes to the weapon you kill with. Like, if you need 500 xp to get to level 2 with a weapon, that would be 5 kills in a tdm/kc. If so, double xp should correlate directly to weapons as well. Maybe do a search to find out how weapon xp works.
So I was gonna give it a go again this weekend and played last night to get a feel of it as I haven't played in a few weeks. Logged in to play after knocking out the plat for FFXIII, went 40-8, signed out and turned it off. Just boring and I can't see my self playing it anymore.
If the xp is stackable, is there a limit? If I had 5 coins plus double xp weekend that would mean times 20? Sent a tweet to bowling asking but not sure if that was the right person to ask... just saw his name at the top of this thread. :-D