There is a malfunction in the system that we have not been able to identify. Some people still get their notices, others do not. We cannot tell why.
The system involves over 10,000 lines of code that we did not originally write so it has been unbeleivably complicated to try to debug it.
The plan right now is to upgrade the vBulletin version 3.0 when it is released (in the next month or so). That will fix any problems with the email notices. It actually has a much better email notification system.
You have the ability to get notices in forums that you have not posted in and you can specify whether you want immediate updates, daily or weekly updates on the forum. If you ask for daily or weekly updates on a specific forum or thread they will come in the same email, not separate.
We are highly anticipating the new version and are preparing to upgrade right now. Hopefully it will be released soon.
I will keep everyone posted.