Datatypes rock. No other system I've used handles data formats quite as elegantly.
My only criticism is that theyr'e not bidirectional. An encode method in the datatype system would be very cool.
How nice it would then be if you could load a jpeg etc. into multiview and could save as any other (pixel based) image format you had a datatype for.
Definately something I want to see in later versions of the OS :-)