In my presentation I will show several delegate controls that exist in SharePoint OOB (WCM and WSS master pages) in SharePoint designer, and speak shortly on the possible uses of these controls.
I will also show where SharePoint uses this trick to change the search box in a WSS site once you connect it to a search center.
I will share (presentation only) the code of an existing product we have that shows:
1. How to develop a new search control
2. Code of the feature that registers it to replace the SharePoint search box
3. Activating the feature replaces the SharePoint search box