Object performance vs Caching

With the new object oriented drive in .NET, how big of a performance hit do you think it is when you access the methods of simple objects?

For example

Color.ToArgb
Point.X
Point.Y

How about arrays? Is it slower to access a variable in an array than to access a non array variable?

myArray(2) vs myVariable


Where do you draw the line when it to comes to caching local variables?

Any thoughts on the matter are welcome. :D