Interesting issue I discovered tonight...
I changed my home router, and I wanted to remove the old settings from my iPad (iOS 6.0.1). I was able to do that easily with all my other devices--just select the wireless network and click or tap "delete"/"remove"/"forget"/whatever. However, I couldn't find that option on the iPad.
I did a little Googling, but none of the results matched exactly what I was trying to do. However, one article I read said that while a lot of people are seem to be having network problems with iOS devices upgraded from iOS 5.x to 6, the issue isn't the network drivers, but instead, that the network settings seem to get corrupted during the upgrade. The author suggests the easiest way to remedy that is to go into Settings > General > Reset > Reset Network Settings. This basically deletes all configured wireless networks.
I did that and reconfigured for the current router. Then, I noticed my VPN entry was gone (which makes sense). I reconfigured VPN per the settings in the Sonic.net wiki, then tried to connect, and I got an instant connection.
This makes me wonder if the problems some of us are/were having with VPN on iOS devices upgraded to iOS 6 is also due to corrupted settings as a result of the upgrade.