About 2 years ago, I developed an application which supports user to "draw" rectangle and line by mouse at runtime. They need to handle some events (like double-click, right-click), also user can change its background color, set its background image, and do something else. At that time I made them as user controls 'cause I found that Microsoft didn't provide Rectangle and Line controls.
The revolution of API (Why do they make it lately?)
A few days ago, I found that in .NET Framework 3.5 SP1, Microsoft will provide several vector shape controls (Rectangle, Line, Oval,...) for all languages.
And the lack of knowledge in API
Also a few days ago, I found that Microsoft already provided Rectangle, Line controls but only in VB.NET (Microsoft Visual Basic 2005 Power Packs 2.0). If I could found it long time ago, I would not need to spend too much time in creating the user controls. (Yes, I know I can use them in C# even they are for VB.NET)