The SharePoint 2010 Developer Platform: An Introduction for ASP.NET Solution Architects
SharePoint 2010 also provides an application platform. This platform relies on ASP.NET and other .NET Framework technologies, but it adds plenty of SharePoint-specific functionality. A developer creating an application on SharePoint will use ASP.NET, but he'll also use other services that the platform provides. Because the SharePoint 2010 application platform is based on ASP.NET, learning how to use it isn't a huge leap for ASP.NET developers. But when does it make sense to build an application on SharePoint rather than on raw ASP.NET?