I listen to DotNetRocks regularly, and I was surprised on a recent episode when Carl did his "Better Know A Framework" segment about the ApplicationException class. He stated it was no longer a good practice to use it as a base for all of your custom exceptions - something that I hadn't heard.

So I did a quick search, and lo and behold, Carl was right. Here's a post from Tobias Gurock stating the same thing from back in 2005, referencing a post from Brad Abrams back in 2004.

I guess I'm a bit out of date.