Unfortunately if you want to go to SDCC, you really have to plan pretty far in advance. The full four-day(+preview night) passes for 2011 sold out at last year's convention, if I remember correctly. And that's without factoring in how fast the hotels book! I'm fortunate in that I have a friend with a house not too far off.
It's actually very odd from a press perspective, because they don't open press registration up until 1-2 months before the event. Their press requirements are fortunately not very demanding (in my experience), because if you waited for press reg and got denied, you'd pretty much be screwed out of going (unless you also got a paid registration).