I heard from an active Witness last year that Governing Body member Anthony Morris gave a talk at their assembly (I can't remember if it was a circuit or district) in which he specifically mentioned myspace.com. This was a particular concern of the Governing Body; and the GB was quite aware of many teenage Witnesses posting on the site, as well as several Witness groups that had been set up on the site.
According to this active Witness, Morris was very emphatic and blunt in telling the youths (as well as anyone else) to immediately stop using myspace. It wasn't even considered a conscience matter.
This is a very tenuous postion to take given the fact that so many people use the internet to network for jobs and business. Are they now going to tell Witnesses not even to join any kind of online trade groups or networks? Where do you draw the line?
I guess the prohibition of myspace.com is just one more entry into the Watchtower's great Talmud of legalistic do's and dont's. Personal, Bible-trained conscience be damned.