SharePoint 2010 changed a lot of things about security trimming from 2007. I've implemented the new ISecurityTrimmer2 interface, and I've registered my trimmer with SharePoint (following the suggestions here). However, my trimmer is not consulted during a search. There are messages in the logs about security trimming, like "PluggableSecurityTrimmerManager:SetSearchApplicationToUse: Set SearchApplication to 'Search Service Application'". Any ideas what I'm doing wrong? Is there a necessary step in addition to registering the trimmer? If it matters, I'm using BDC to allow SharePoint to crawl my content, and this part is successful.
Most of the documentation on the web deals with registering security trimmers using PowerShell. For ease of deployment, I'm registering from C# code running during installation. One difference in the approaches which may explain the behaviors is that the PowerShell command takes a crawl rule, while the PluggableSecurityTrimmerManager does not.