I first started in VS2005 by copying existing VS2003 files into '05. When I started creating new forms and usercontrols I noticed these someform.designer.cs files. VS2005 was acting a little squirrely at the time so I wondered if something might be broken. Then I discovered they were partial classes and containing all of that "Windows Forms Deisgner generated code" stuff that normally clutters the form.cs file. So I rewrote the VS2003 forms as partial classes to take advantage of the idea of keeping the designer stuff separate from the more interesting logic in the form.cs file. Much easier and cleaner to work with. Here's a sample someform.designer.cs to explain what I'm talking about.