Just thought I'd share something I found about Cpanel 11 for the benefit of others who may have the same problem...
The converted filter rules worked fine for me after the upgrade... UNTIL I made a change (I deleted a filter). Once I did this, all the converted rules stopped working, and instead of sending certain messages to an email address as they used to, messages that matched the filters just disappeared. To fix this, I deleted all of my converted rules and re-created them. This wasn't too bad, considering the filtering is much nicer in cpanel 11. However, I wish I had known to do this yesterday so I wouldn't have lost an entire days worth of mail that should have been delivered to a different address according to my filters. (I use these rules extensively to filter potential spam from my users, in addition to spamassassin).
Just thought other people may want to know this!