We have been working with iOS 8 since the first Beta and are happy to say that curbi works just fine with iOS 8.
The problem is that the iOS upgrade process wipes the curbi VPN password so that after upgrading your device won't be able to get to the curbi VPN servers.
This bug appears to be fixed under the iOS 8.0.1 upgrade, so things may improve when that is released.
We sent out an email to everyone who had a device enrolled in curbi, so hopefully that made it through. We have also put up specific instructions on how to upgrade from iOS 7 to iOS 8. The bottom line is - unenroll your device from curbi before upgrading.