Attendee registration for Comic-Con International 2011 will open this year (again!) at 9 AM Pacific Time on Saturday, February 5. Here is the information you'll need to know.
If you're thinking of going but aren't sure, consider this. The con will sell out and it will sell out very quickly. If you decide in May you want to attend…well, it won't be utterly impossible but it'll sure be difficult. After they officially sell out, some badges will become available as their purchasers cancel and get refunds but I sure wouldn't count on being able to snag one of those.
Also, the convention has been cracking down on folks who sell badges on eBay or elsewhere, some (maybe most) of which are counterfeit. There was criminal prosecution last year of some who sold them and there were people who bought badges via bootleg methods who showed up and were rightly denied admission. That will be all be policed with even greater efficiency this year. Don't even think of going that route.
I'm well aware it may be tough in February to know if you'll be able to attend in July. Will you be able to afford it? Will your employer let you have the time off? Will you be able to find lodging? You may not be able to answer those questions right this minute or even by the time the badges are all gone. All I know is that if I had the choice, I'd rather be someone who had to get a refund later on, as opposed to being someone who decided to go and couldn't buy an admission then.