As someone who had (most of) the Red Wedding spoiled myself, I can say that it didn't impact my enjoyment of anything at all. As it stands, the Red Wedding really was only the tip of the iceberg, and from then on everything else just got crazier and crazier.
I did have something about the ending of
Dance involving Jon vaguely spoiled for me via a conversation I was having with someone who read the book on release (damn it I really need to read faster) a while back, and while it's a bit annoying having certain things like that in the back of my head it hasn't really impacted me while reading thus far.
That being said, I'm really looking forward to being able to go into the next volume completely fresh, whenever it eventually comes out. Hopefully next year, since this year is probably asking for way to much.
Right now, last thing I read was
Spoiler
Victarion getting his new burnt arm from Moqorro. Pretty awesome stuff