The Exact Editions system now makes ISBNs clickable and the first examples (for subscribers only, as the issue is behind the subs pay-wall) are in the current issue of Opera magazine.

This is the example that I tried first:

January 2008
Page 95

Which today takes you to this page. ISBNs have recently gone to 13 digits (that allows for a lot of books and publishers) but Amazon is currently using a look-up table for the 13 digit numbers, which is why you land on a results page. Currently we target the Amazon UK pages by default, but this should become a configurable option.

Clickable phone numbers and clickable ISBNs……more good things for the iPhone.