My experience with OperaMini is that, there are two types of failures with socket protocol enabled.
1) Socket protocol fails a half day or so after a reboot. A reboot fixes the problem. No restarting of the Data Services or the Mobile Network seems to help fix it, only a reboot. This would seem to be a problem on the blackberry itself.
2) Socket protocol fails and even reboots don't get it working again. This happens more often than I'd like and I'm guessing that it's either the opera proxy servers being down or unreachable through your provider. Usually, within hours to days, with no intervention on your part, it all starts working again.
In both cases, if you want to avoid a reboot or waiting switch the protocol in OM to HTTP so it connects through BIS the way most other apps on the blackberry do. This of course makes for slower browsing, but it's all that works sometimes.