I went to El Celler de Can Roca recently - and reserved a mere 11.75 months prior to that - so I figured why not leave a report of my experience here on Chowhound, my go-to source for planning trips. (Because what else is there to plan besides where to eat?) Just in case anyone else is thinking of going or curious.
I have heard that they get cancellations the same day, so if you don't want to reserve so far in advance, it looks like it's definitely worth trying to get on the wait list or at least calling in about cancellations just before.
I would put the entire report here in the post, but there's lots of photos, so if you're interested: