It seems as if the five billionth tweet has been tweeted (twittered? tweedled? en-twittenated?) from micro-blogging site Twitter.
As you can see, the "Pentagigatweet" reads only "Oh lord.", and it originates from Robin Sloan, a California writer and "web generalist." It's not a religious expression; Sloan's "Oh Lord." is the reply to another tweet.
Of course the accuracy of the five billion number isn't definite. It's based on third-party app Gigatweet's calculations, and doesn't take into account the times Twitter reset the tweet counts, nor does it factor in pre-launch tweets. But still, Sloan has the number 5,000,000,000 in his tweet's URL, and that's good enough for me.
As for the future of the famous tweet: Sloan promises to unleash the power of the "Necropentagigatweet" tonight at Midnight, PST, when he deletes the five billionth tweet from existence. This will most likely destroy the universe.
Sadly, my latest tweet, is not notable in any way.