More on non-visual controls and the component tray
Daniel Cazzulino uses strong words to express his anger over the disappearance of the component tray in the ASP.NET designer.
Nikhil gives an excellent explanation of this and why data sources are controls (to summarize really quickly, they must be part of the page lifecycle).
This also answers an ongoing discussion on TSS.NET about the SqlDataSource, on a subject similar to this old blog entry.