Ian Griffiths takes an in-depth look at C# 3.0 Extension methods and the potential problems with it. Of particular note is his philosophy, which directly follows from the idea that code should be written for humans, which he summarizes whe he say...
I’m a big fan of code that does what it looks like it does.
Amen brother!
As an example, he highlights the ToUpper method on a System.String instance, which often misleads new developers. He would prefer the more honest and less misleading static method on the String class that would be called like so:
String.ToUpper(input);
I agree wholeheartedly that ToUpper (which sort of follows the Java convention I guess) is misnamed, but (and this really is a minor niggle) I probably would prefer that it still be an instance method, but renamed GetUpperCase. I think that would do a good enough job of being honest and being discoverable.
In any case, if you’re interested in C# 3.0, be sure to read Ian’s take on extension methods.