Bob has excellent post explaining ease of using content types and rolling them up with Content Query Web Part:

http://bobmixon.com/BLOG/archive/2007/10/25/Getting-More-from-the-Content-Query-Web-Part-CQWP.aspx

Here is the post of customizing CQWP for extending its OOB functionality:

http://www.heathersolomon.com/blog/articles/customitemstyle.aspx