I hadn't used this yet, and had cause to this week.  It works slick, and is pretty configurable... I used it to hide the SiteActions button on list pages for members, but not admins, as well as admin web parts embedded in a page.  It works with Web Parts, Web Controls, and other ASP.Net objects (ie. SharePoint:*, etc.).  Wrap the content you want trimmed in the following code (using SPD):

<Sharepoint:SPSecurityTrimmedControl runat="server" PermissionsString="BrowseDirectories">
[Content to Trim]
</Sharepoint:SPSecurityTrimmedControl>

You can then swap out the "BrowseDirectories" with whatever you need for the trimming.  Here are the one's I've found handy so far:

• BrowseDirectories = Anyone but Limited Read (Anonymous is Limited Read)
• ManageWeb = Site Collection Admins
• ManageSubwebs = Site Owners
• AddListItems = Site Members and specified list contributors

Here's a link to all the defined values in the SPBasePermissions Enum.