Yeah, it's hard as hell to avoid spoilers. I should probably stop going on Tumblr, but I just keep going... and, despite the fact that I have all posts with "pokemon" in them blocked, I still see things. And, every once in a while, click through to a post that has spoilers that aren't as clearly marked. That just happened to me, spoiling what I think might have been a Legendary. So... yay.
I don't think it will ruin half the fun, though. It's a huge bummer, to be sure, as Pokemon games are at their best when going into them near-blind, but the games will still be a blast. Just think of accidental spoilers as little tips given to you by a friend who got the game before you. Or something.