A Great Start
I started reading this story arc from issue #249 and it was so compelling I had to order a copy of this issue. Man, it REALLY makes me want to pick up Age of X when it comes out on trade paperback.
So, as it explains ni the opening pages, the X-Men were sucked into an alternate reality and when they came back, they still had those memories in addition to their original ones. It's making it very hard for them to cope and is messing with some relationships. The results that start here in #248 are still being felt in #251 and may perhaps even end up contributing to confusion if X-Men Legacy ends up tying directly into Schism this summer. Definitely get this issue.