They have around 25m users according to TC. that makes it about $28 per user. Which is alright, I have seen higher numbers per user.
Are those active? I've heard a lot of Twitter's "users" sign up but aren't posting.
Also some people create 650 accounts ;)
But seriously, if the company is making no revenue, that sum is just for the user base. So how much does that make the value of every user? (does anyone have a current user count for twitter? I could only find figures from February but I imagine its much higher now.)