The full royal decree:
"Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 4.24pm. The baby weighs 8lbs 6oz. The Duke of Cambridge was present for the birth. The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news. Her Royal Highness and her child are both doing well and will remain in hospital overnight."
So that's that. There's no word on a name yet, so the media's obsessive coverage and speculation will have a reason to keep burning brightly for the near future.
The early takeaway from today, I suppose—not counting the royal family's nearly unrivaled ability to keep news a secret until they're good and ready to share it—is that the birth of boy means that the rule change that became British law earlier this year keeping a female child from losing her spot in line for the throne to a younger brother won't be put to use if/when Kate gives birth again. (Note: The law itself still needs to be ratified by other nations in the Commonwealth.)
This post has been updated with additional information.