Five years and one week ago, Twitter cofounder Jack Dorsey sent the first ever tweet: “inviting coworkers.”  Now, to celebrate the occasion, Twitter has shared some stats about what’s occurred since then, and the growth rate is extremely impressive in almost every respect.

Twitter’s Carolyn Penner posted the data on the Twitter Blog, and she began by talking about the rate at which tweets are sent.  Apparently it took three years, two months, and one day for users to write the first billion tweets.  Now users post a billion tweets every week (on average).

Next, Penner addressed the subject of user accounts.  She indicated that a whopping 572,000 accounts were created on March 12th, up from a still-noteworthy 460,000 accounts on an average day last month.  Also, Penner said Twitter’s seen a 182 percent increase in mobile users over the past year.

Finally, Penner wrote, “8. 29. 130. 350. 400.  Number of Twitter employees in Jan 2008, Jan 2009, Jan 2010, Jan 2011 and today.”

So Twitter appears to be in good shape.  Growth of that sort is something that only a handful of companies can match.

Of course, we should point out that there wasn’t a single dollar sign in the entire blog post, meaning Twitter’s still being shy about sharing its financial info.  Less specific information about advertisers was absent, too.