Say I wanted to pick up an Avengers comic off the shelf, or for instance pick up the Avengers vs X-men comic when it's released. What's the Minimum Background Knowledge I'll need to fully understand the characters?
I realise that marvel will be wanting to make this comic open to a new audience, but I'm sure there will be some thing I'll miss due to not being in the loop and up to date.
Which stories have shaped the Avengers, especially the ones whose effects are still being felt today?
Easy answer: Read up on Wikipedia.
Long answer: You could probably go all the way back to Avengers: Disassembled, if you really want to be thorough. Bendis has said that he is tying together all of his writing into a sort-of long story. Then on to House of M, Civil War, Secret Invasion, Siege, Fear Itself. Then start on the X-Men event Schism.
I would say that for a specifically X-Men/Avengers history,just read House of M. That's probably the most significant X-Men/Avengers event in recent history.
Modern Avengers:
I'll just recommend what I started with which is Avengers Volume 1 & 2 and New Avengers Volume 1 & 2.
Both were written by Brian Michael Bendis; the comics started in 2010 I think.
'Fear Itself: Avengers' is essentially volume 3 of both titles
Although the next volumes of each series are titled Volume 3 and are available in May, which I guess makes the Fear Itself book Volume 2.5.
I would only go back as far as 'Avengers Disassembled' if you really have to know everything and have a lot of spare cash, but as far as getting to know your cast I'd simply stick with the current run.
Avengers Movie Starting place,
I would read The Ultimates comics where Marvel did an excellent job modernizing the Avengers story. They were a reluctant group of individuals who came together to fight against an earth ending threat. I believe was the inspiration behind the plot of the Avengers movie. http://en.wikipedia.org/wiki/Ultimates
