[tsm]

Many SICP exercises would be similar to, "Ben Bitdiddle thinks he can define COND like this: [bunch of code]. Show why he's wrong." Which is not practical whatsoever--it's clearly a short problem for academic purposes.

In contrast, PCL would say, "Now we can write a media server, let's go!"

[djcb]

It's the difference between understanding and copy-pasting.