Where did Forrester get its Twitter data?

Peter Kim of Forrester writes on his blog “Our data shows that 6% of US online adults use Twitter regularly.”

I say bulls**t.

There is ABSOLUTELY NO WAY that many people are using Twitter.

My data shows that the regular users are between 50,000 and 300,000. A high percentage of which are outside the United States. That doesn’t come anywhere close to the numbers required for 6%.

Keep in mind that Hotmail has about 200 million users every month. Yahoo Mail says they have about 250 million worldwide users.

But, I’d love to be proved wrong. Where did this data come from? How was it collected? Does Forrester stand behind it? What’s in the report that Peter linked to (I am not a Forrester client, so don’t have access)? Does it contain other numbers that just don’t jibe with common experience?

UPDATE: Someone just Twittered me this: “Peter Kims’s source on the unique users (he says 447,000 in Aug07) is Nielsen//NetRatings.” I doubt that’s data for “regular” users, or even online adult users in the US. I could see total registered users being that high, but that’d be world-wide. Watch twittervision.com someday and you’ll see that there are lots of users outside America.

UPDATE 2: Peter Kim responded here, and says they didn’t get the data from Nielsen. I still think the survey is very flawed if it’s bringing back such numbers.