GigaTweet (no affiliation with GigaOm) tracks the total number of tweets tweeted, in real time. It also aggregates tweets per hour in millions, and gives a few months of historical data. Guess the total number of tweets? It seems that 4.88 billion tweets have been written.
That is a lot of spam and bathroom updates.
It is almost hypnotizing to watch the numbers spin towards five billion. As of right now, 4,888,639,386 tweets have gone live. But, by the time that you read this, that number will be far out of date. Check out the application here. They have a selection of higher resolution graphs here.
Oh, and help the crusade to five billion by tweeting this story, of course. H/T JeffJarvis.