Although the post is ostensibly on Extension Methods, as with many of Ian's posts it has a lot of useful stuff to say about other things:

As I've said in the past, one of the great tragedies of the current crop of mainstream languages is the bizarre and awkward construct we call inheritance. It conflates two very important but really rather different concepts: reuse and polymorphism. When you stop and think about it, having one solution that attempts to address these two requirements is a bit bizarre.

Enjoy...