Here's an interesting article.
In this one, a US District Judge says explicitly that
the first amendment does apply to the internet and that
people DO have a right to anonymous speech online.
The case involved a company claiming that users of a
chatroom had "conspired" to drive its stock price down
so that they could profit by shorting the stock. The
company demanded of the operators of the chatroom the
identities of the people involved. The judge refused.
The article may be found at: (look out for line wrap!)
http://www.sfgate.com/cgi-bin/article.cgi?file=/news/archive/2001/04/20/national1133EDT0546.DTL
I think that if the company had presented compelling
evidence of the conspiracy, the judge might have ruled
the other way -- he mentioned explicitly that the evidence
against these nyms was mainly "innuendo". Does that
mention indicate in legal convention that otherwise he
might have issued the subpeona?