That's technically inaccurate. I've seen them. But I haven't comprehended them. I think someone died. I honestly couldn't tell you who.
And I haven't been avoiding the Internet in any way. I've been reading friend's pages. I've been reading Slashdot. I've been reading SomethingAwful, including the Goonfleet forums, and lemme tell ya there have been tons of spoilers posted on those.
What's the secret? It's pretty simple. I haven't read Harry Potter yet.
Now, that isn't to say that Harry Potter is bad. I'm not going to pull a "ha ha, I haven't read it, and therefore I haven't wasted my life like you suckers who read things that you enjoy" line. I've heard it's quite good. I plan to read it. But the fact is that I know essentially nothing about it. I know there's a character named Harry Potter who goes to this magic school, and meets these characters named Snape, Voldemort, Hermione, and Beasley. I may have the last one misspelled. I only know it because of Potter Potter Potter. I also know there's some crazy sport involved somehow, though I don't know how important it is (quiddich?). I don't know anything else, and so when I see people posting "OMG ____ died lol now it's spoiled for you" it just slides off. I don't know who that character is - I'm certainly not going to remember it.
I'm doing the same thing with Battlestar Galactica. There's Cylons, see. And . . . apparently it's a cool series. And right now I'm largely immune to spoilers, simply because I know nothing about the series. I know people have tried. I've read things that were Battlestar spoilers. Can't say I remember them, though.
Obviously this isn't perfect. The downside is that I haven't read Harry Potter or seen Battlestar Galactica. But it's not spoiled for me, and by the time I get around to reading it, nobody will be trying to spoil it.
Next time you see something upcoming which may, in fact, be awesome, try avoiding it for a while. Pick up something else that you've heard is awesome. Once the new series is done, then go read it. Remember, you can always decide to change your mind. Unfortunately, there's No Going Back. I'm reading the Song of Ice and Fire series. If someone spoils it? Man, I'm hosed. I can't just not read the next book. I'll still know the characters. So I'm stuck on that one - but I can still avoid future serieses.
Your mileage may vary, of course.