A colleague, Fernando Felman has highlighted a very useful and interesting blog spot by Andreas Grabner that walks-thru scenarios and looks into the performance of SharePoint when under various SharePoint object model calls.
Though quite a few points in the post are obvious to the developer, I still think it is worth a good read :)
The article:
SharePoint Object Model Performance Considerations
http://www.infoq.com/articles/SharePoint-Andreas-Grabner
