If you were quick enough to get on the court's site before the servers were overwhelmed, then you already know why Judge Vaughn Walker denied the motion to stay his decision in Perry v. Schwarzenegger. Judge Walker found that the proponents of Proposition 8, California's ban on gay marriage, did not meet any of the four requirements necessary for the court to grant their motion for a stay.
In the Order, the court dealt in detail with each of the four requirements necessary to allow it to grant a stay: will the parties seeking a stay be likely to win on appeal; will parties seeking a stay be irreparably harmed if the stay were denied; will a stay harm any other interested party and will the stay, if granted, be in the public interest. As required by precedent, Judge Walker focused most strongly on whether or not the proponents of the law met their burden in the first two requirements.
Judge Walker found that the proponents did not show a likelyhood of success on appeal. Not only did he cite what he said was a paucity of evidence in favor of the state's interest in upholding the law, but he cast doubt on whether the proponents would even have standing to appeal, unless the state was brought in as a defendant as well. The judge also could not find any evidence of direct harm to the actual proponents (who are not state agents) if the law was not upheld. Finally, Judge Walker found that to allow what he has found to be an unconstitutional law to remain in effect would directly harm the opponents to the law and was not in the public interest.
In the end, the New York Times may have put it best when they wrote, "Same sex marriage is legal again in California. Sort of." Despite today's order from the court, there will be no immediate granting of marriage licenses in the state of California. The judge has stated in his Order that the state's cessation of enforcement on Prop 8 will not begin until August 18. This allows the proponents of the law time to appeal his denial of the motion to stay to the 9th Circuit. For now, despite what seems to be a sea-change in the law in California, it is just more of the status quo.