All tickets--even single-day tickets--sold out for SDCC months in advance.  SDCC is crazypants.

it was worse than that this year.  When they went to sell tickets, their site crashed twice.  They then went to Leapfrog to sell the tickets, but even borrowing server space from Amazon.com wasn't enough.

The system was cleary overloaded.  Had to refresh at each step of the process to get anywhere.  Glad I had the day off, since it took 2 hours to sign up.

Think they sold out in a matter of hours.

(Of course, this doesn't count the at convention passes.  Which are sold at show.  However, the show is so popular now, those seem to be unfair to those who can't attend.)

Update:
While tickets aren't currently available, apparently more passes will be for sale in the near future.

At this time we expect to have 1,500 4-day badges available for purchase.

http://www.comic-con.org/cci/cci_reg.php

(BTW: Has there been any update in regards if Jim will attend?)

I'd say chances are better of seeing Jim at a smaller event (than SDCC).  I tried catching a few authors back in 2009.  Had to stand in line for an hour or so and draw a ticket (winners had an "X" on it or somesuch).  I didn't stand a chance.

But at other events mentioned here, it seems there's more of an opportunity to not only get an autograph and ask him a question, but to actually attend the occasional event with Jim as the honored guest. (Can't speak for all events and activities, of course.)

Aside from that, even if Jim is unable to go to SDCC, it'll still be an amazing con to attend.

Of course, the point is somewhat moot.  Since they sold out of SDCC tickets in a day.  Of course, last year a number of tickets were made available right before the convention, but there's no guarantee on getting them.  I'm going this year, but it wasn't at all fun Saturday & required a lot more refreshing than you'd expect.

Kevin