Jane Goldman who helped script Kick-Ass is apparently doing the same on X-Men: First Class.
Jonathan Ross, or @wossy, is the outspoken English TV host and comic book/movie supergeek who happens to be married to the charming and wicked-smart Jane Goldman. She was Matthew Vaughn's co-writer on both "Kick-Ass" and "Stardust," and based on my time watching the two of them together on-set, I'd say that she's a key collaborative part of Matthew Vaughn's process. The script that the two of them wrote for "The Debt," a Helen Mirren film that is still looking for a release date, is probably the strongest thing they've written together yet, and a clear indication that they're capable of far more than just post-modern comic book riffing.
About the same time that Matthew Vaughn was confirmed by Fox as the director of "X-Men: First Class," Ross posted something about how his wife's new job would keep her busy for the next ten weeks.
I tried to verify the news through the regular channels, but before I could even get a response, Ross did it himself. Today, he posted that his wife is away from home working on "X-Men 4." Okay, then. Unless we hear that they've broken the team up so Goldman can write a future X-Men film with Matthew's working on "First Class," I'm going to take this as confirmation that Vaughn is indeed customizing this movie as he works to get it ready for a mid-summer production start.
The full article goes into a little more depth about the scripting process of the film so far.
Bringing Jane aboard works for me, aside from liking her work on Kick-Ass, it means that Vaughn apparently has a good amount of creative control on the project.