Look, I know that nobody likes waiting for these things, and that the wait is only exacerbated by the attention and analysis that's paid to these types of projects throughout pre-production and into the casting process. (And yes, clearly I'm guilty of perpetuating that system here.) However, when you wait all that time to catch a glimpse of footage, to finally see the director's vision for the latest iteration of your favorite character, why would you want to watch it through someone else's iPhone? It's like spending all day marinating a really nice steak, watching it grilled to perfection, cutting off your first bite, and then dipping it in motor oil before it hits your lips.
Not only do leaked trailers do your eyeballs a disservice, they're also an insult to the movie itself. The filmmakers and studios are very careful to craft an introduction between their work and public, doubly so when it's something as iconic as Spider-Man or The Avengers. They want to blow you away the first time you see that webhead swinging through the streets of NYC. They don't want you to squint at a grainy composite, tilting your head at a 45 degree angle, trying to figure out exactly what it is you're even seeing over the back of someone's head.
Trailers live on the internet now and I have no problem with that. In fact, I love it. But let's try exhibiting a little patience folks. (Especially with Spider-Man and Avengers. You really don't think you'll see one or both of those trailers in front of Captain America this weekend?) If you're not going to wait to see a trailer in the theater, (where you might actually be SURPRISED at what you're seeing, i.e. the first Muppets trailer) then at least hold out for a proper, full screen HD version.
I promise you, it'll be worth the wait.