Only 24% of twitter users have supplied biographical details in their profile

Usership stats:
"24.14% of users have a bio in their profile
31.32% of users have a location in their profile
20.21% of users have a homepage URL in their profile
45.12% of users have tweeted at least once
47.29% of users have at least one follower
44.50% of users are following at least one account"
The average user:
"The average user tweets .97 times per day
The average user has tweeted 119.34 times in total
The average user has a following-to-follower ratio of .7738"
Source: Hubspot State of the Twittersphere report, June 2009