in reply to [Opinion] RT versus OTRS
Local customizations were pretty simple once you learn how the overlay system works, and interfacing it with external code isn't too difficult either. We've got a script that scans the incoming ticket queue and associates each one with the appropriate customer account in Salesforce for the sales team (using the Salesforce SOAP API), and an RT query module for mozbot so we can grab basic ticket status via IRC.
I've never used (and until now, never heard of) OTRS, so I don't really have much to say about it. However, I notice that they use Bugzilla for their own tracking, rather than eating their own dogfood.