Each of the four previous volumes in A Song of Ice and Fire is notable for being released in the UK before the USA, in the case of A Clash of Kings over four months earlier. Obviously this had problems with spoilers being available online for the books long before the American edition of the novel came out, so for A Dance with Dragons Bantam had carefully coordinated its release so it would come out in all relevant territories on the same day, minimising the risk of spoilers. They also put in place a review embargo preventing reviews from appearing in the press until just before release day.
Typically, these plans have been fouled up by an administrative error. For a few hours earlier today, Amazon.de (the German branch of Amazon) was selling copies of A Dance with Dragons for immediate dispatch. Word spread and a number of fans, including some in the USA, were able to order the book before Amazon realised what was happening and reverted the date back to the official release day of 12 July. Unfortunately (for the publishers), they appear to not have been in time to stop a few of the orders going out.
So, in a day or two, expect to start seeing discussions of A Dance with Dragons appearing in various corners of the Internet. All of the major fansites will likely put into place spoiler warnings for any discussions that take place, so it's a good idea to keep an eye out for such warnings. I've already heard some extreme spoilerphobes vowing not to log back into the Internet until after the book's official release date, which seems a tad drastic, but given the danger of being spoiled at the last minute having just waited six or indeed eleven years for this novel, this is somewhat understandable.
This blog will continue to be an ADWD-spoiler-free zone until further notice, however :-)