This was apparently the introduction to CRC cards that was supposed to come before the article last week that talked about them.

I think one of the most useful things about the CRC cards is that, like it says in the article, they allow you to make the design of a system more concrete. For many people, especially kinesthetic learners, a technique which allows you to put your objects down on a table, and move them around and organize them, is probably extremely useful.

Various software pacakges, such as XOMT and Rational Rose, seem to be computerized versions of this sort of exercise. They allow you to visualize class relationships, and move them around, except they are screen representations rather than pieces of paper. I think for people who consider OO design to be very abstract, these methods would help them.