Well the author says in the conclusion that they don't think that they're particularly readable, but from an artistic point of view they're definitely more interesting.

Even if it isn't a success, I would like to encourage this kind of experimentation with data visualisation.

I agree with Stuk, data visualisation is all about capturing the users attention and interest besides giving out information . Maybe its not apt for a police station soft board but a junior school teacher on the other hand might find it useful

You sound as if "giving out information" is a secondary goal of data visualization, while I would argue that capturing the user's attention and interest are.

Just out of curiosity, what does a circular 24-hour clock look like? Midnight at the top, and noon at the bottom, where 6 o'clock would normally be?

The benefit is in avoiding the confusion that comes from mapping a new concept (a 24-hour clock) onto a very familiar, almost instinctual one (a 12-hour clock).

most 24-hour clocks and watches have 0 or 24 at the top. i've seen a few with 0 at the southern-most position but they are not very common.

here's my watch:

http://www.flickr.com/photos/symmetricalism/5703135927/

You guessed right. If I wore jewellery I'd wear 24 hour watches: http://www.xs4all.nl/~andres55/cosmonaute1.htm