Seems that Blizzard was indeed not prepared for the onslaught.  As it currently stands Blizzcon tickets sales are on hold until the issues on the Blizzard Store site are dealt with.

A Blue posted the following in the WoW Forums:

This is top priority right now, and we are still actively looking into this issue. I can tell you that we have confirmed that no tickets have been purchased at this time, so no one should fear that they are going to be sold out while they are refreshing.

I’ll continue to try and provide updates as we get them, guys. I know you’re frustrated, thank you though, for remaining civil while we sort this out. It is appreciated. :0)

Just up on WoW Insider:

http://www.wowinsider.com/2008/08/11/blizzcon-tickets-on-sale-kind-of/

It's Monday, August 11th, and that means that BlizzCon tickets are on sale. Except, they're really not. Blizzard's new Blizzard Store site is epic fail broken -- all most people are seeing is the "error has occured" screen above.

Hopefully this isn't a preview of things to come. and hopefully Blizzard will figure out a fair way to get these tickets out (because right now, the site certainly isn't working). Expect more updates to this post as the process goes along.

Update: Seems like a lot of people are making it to the credit card verification screen before things go bad, so it seems (seems) the fault may be with the credit card approvals, not necessarily Blizzard's site. Also, one big change from last year is that not only do you specify your WoW character during checkout, but they ask you to say your favorite Blizzard franchise, as well.

Update 2: Alex here, seems the entire site is FUBAR pretty much. Definitely not a credit card thing. It won't even let me shop for books to add onto my order.

We're liveblogging our quest for BlizzCon tickets -- lots more updates after the jump.

More info will be posted as it is released.