One of the most frustrating aspects of SharePoint administration and development is the inability to get any sort of granular performance metrics for page objects (especially web parts). SharePoint can be a finicky beast - configure a setting wrong here, make the wrong object model call there, and performance slows to a crawl. Identifying which objects on a page are causing performance bottlenecks is more art than science, requiring a great deal of back and forth between development and IT, resulting in a tremendous amount of finger-pointing and lost productivity.
To meet this need we have created the Sonar suite of performance measurement tools for SharePoint.