>>36702576AvX isn't that far in. It started with Avengers: X-Sanction, which was a mini-series about Cable crashing the scene. It's 2 issues into the main series.
There are tie-ins with Wolverine & The X-Men, Uncanny X-Men, X-Men Legacy, Avengers Academy, Avengers, New Avengers and Secret Avengers. Out of those I'd only recommend Avengers Academy, Uncanny X-Force and Wolverine & The X-Men. I've heard Secret Avengers is alright, but I've never checked it out.
There's a series called AvX: Vs, which is literally just X-Man vs Avenger beating the shit out of each-other for an issue. It's meant to be pretty good, simple and entertaining. Have yet to read.
The event overall is okay. Ish. /co/ hate it, but it's not TOO bad. It's said to have "big consequences" for the Marvel universe.