You can remove the Content tab, as many did with P5, by hacking an XML file. I've always doubted that this truly removes Paradise from Poser, but at least you won't be able to see it any more.

You can block Poser from accessing the 'Net with ZoneAlarm or some other firewall.

Be aware that P6 also has an auto-update feature now, and will attempt to contact the CL server on every third launch to check for new patches and the like. You can disable this feature from your General Preferences menu, if you find it annoying.