Another timely white paper from David Chappell
Yet a SharePoint app is fundamentally an ASP.NET app, so the two worlds have a good deal in common. With the 2010 release, Microsoft has put a significant amount of effort into making SharePoint a better development platform for creating what might otherwise be straight ASP.NET applications.
If you're interested in this area, I've written a Microsoft-sponsored white paper titled The SharePoint 2010 Developer Platform: An Introduction for ASP.NET Solution Architects. The paper's goal is to provide a big-picture view of SharePoint as a platform for creating applications. It's clear to me that with the advent of SharePoint 2010, a significant number of applications that might have been built using plain ASP.NET will instead be built on SharePoint. If you're interested in why, you might find the paper useful.