With the VPN (as long as the IP address is in the US) you get the US version of Netflix, without, you get the Canadian one. Same userid to log in to Netflix, it's the VPN that determines what you get.
If you want a faster/safer VPN to watch stuff on your computer/boxee/iPad/iTouch etc. as well try Witopia. For $40 a year you'll get IP addresses in multiple locations across the globe and also be able to watch Hulu, TV.com, and other US TV on 2 devices at the same time, including the Vox...