There's been a bunch of discussion over Twitter today about getting down to One Infinite Loop on Sunday, June 6th, the day before WWDC starts. Typically, The Company Store (Apple's on-campus store, open to the public) is open that day even though they are not usually open on the weekends. I called the store this morning, and they are going to be open again this year from noon to 5:00pm.
It is not possible to get all the way from San Francisco to Apple's Corporate HQ completely on public transit, so the logistics could be a little daunting, but one possibility would be to charter a bus down. In the long run, it might save some money while being faster and more comfortable.
Chime in in the comment section if you're interested in going from downtown San Francisco down to Cupertino on Sunday, June 6th and don't have a way to get there yet. If there's enough interest, I'll look into what it would cost to get arrange transportation based on the number of interested people.
The other option would be to set up a big carpool.