Hi there. Thanks for your interest in our service.
1) Yes, you are allowed to connect two computers simultaneously, as long as they are from the same internet line. So you can connect both from home, but not one from home and one from work at the same time. Mobile devices do not count to this limit.
2) We haven't seen any confirmation on these allegations that the NSA controls Google DNS, in fact most of the big companies are working on tightening encryption and security after the leaks that showed encryption has been compromised. Additionally, we use Google DNS over OpenDNS as OpenDNS clearly logs data. Google destroys the data after a few hours, and it's pretty fast.
We are contemplating switching over to the German Internet Privacy Foundation's DNS in the future.
DNS Leak Protection is a script that should ensure you do not leak DNS. If security and privacy are a concern, you should enable it. However, the same effect can be achieved by manually specifying DNS In all your network adapters. Thus, if you do not wish to use Google's DNS, manually specify a different DNS in all your adapters and you should be fine.
