I was just reading Jeff Pott's Alfresco article "Working with Custom Content Types" and it is one of the best developer guides on Alfresco that I have read. The article goes through the creation of content types in a step by step narrative with some pointers to other interesting facts along the way. Jeff is hosting a whole series of these articles on his website. The Web Scripts introduction is also very good.
For a vendor neutral analysis of Alfresco's general utility in web content management, I am offering my Alfresco evaluation from Open Source Web Content Management in Java as a stand-alone report. The report covers Enterprise Edition version 2.2, which is due out any day now.