Hi,
I have to guess here, although we know a couple of things from the documents leaked by Snowden. First off, I think this depends on your location, and the type of connection you are making (in the same country vs. overseas).
They have tapped some of the glasfiber cables, we know from the leaked documents. So they might see some VPN connections, even store the communication data. But can they decrypt it? I'd say AES is pretty safe, unless cryptologists say otherwise.
Do they know who is using a particular VPN connection? Most likely not, as they would have to ask your local ISP (every time), and to do that in all countries might be impossible, even for them.
Using a VPN is probably the best option we have at hand to regain privacy...