How many users does Twitter have, really?

Through a pet-project of mine (foratweet.com) i accidentally stumble upon some interesting Twitter stats.

As it’s possible to extract your userid from the twitter-api, giving you a somewhat unique way to check how many users there are on Twitter. Given that they use a sequential userid-system, which many indications point toward.

So, how many does users twitter have?
Using the data from the API i found out the following statistics.

• I created my account back in spring 2007 which gave me userid 704XXX. (http://twitter.com/tommienu)
• I created another account this spring (2009) for a project of mine which gave me userid 26720XXX (http://twitter.com/slashat)
• I finally created an account this Summer (July) which gave me userid 63523XXX (http://twitter.com/foratweet/)

And if this data is sequential, we’re looking at roughly 70 000 000 users worldwide and its approx 100 times bigger 2009 than 2007 with a 10000% user-increase.

This also means that Twitter would have needed to scale their systems with over 10 000%, something we inevitably know that they failed with, which actually gives those numbers some substance.