SharePoint is definitely becoming one of the main application platforms for developers, who can leverage all their existing knowledge of the .NET and ASP.NET to create great LOB and collaboration applications.

What I recently came across is the newly released Patterns & Practices Guide on developing applications for SharePoint that can be downloaded here. Here is a short excerpt of the purpose of the guide:

This goal of patterns & practices Developing SharePoint Applications guidance is to help customers understand how to develop large scale, content-driven SharePoint applications that extend the value of existing line of business systems. We achieve this goal through the Partner Portal reference implementation and general guidance.  …

So, IMHO, if you are thinking about developing for SharePoint this guide is definitely worth to read.