This is what they used to do, but they've gotten more sophisticated - I've been running VPNs for China for my family on EC2 for a while. As far as I can tell, they almost never flat out block an IP. Initially they block a DNS hostname from resolving to a specific IP, then they start filtering out various different ports (including the default VPN ones). You can normally change to a random port and get OpenVPN to start working again, but it appears in the last couple weeks they've been able to identify and block OpenVPN activity on random ports. This happens so quickly, now, that it's pretty futile to try to IP hop unless you can come up with a traffic pattern that is less detectable.
Exactly my experience. I've been running a private OpenVPN instance for a couple of years now -- a month ago they started blocking it. Switching ports works for approximately three hours.
