Ian Bicking: the old part of his blog

Transactions-as-resources are in the O'Reilly RESTful Web Services book

I haven't got the book yet, but "the transaction is a resource" is a pattern spelled out in this review by Jon Udell: http://blog.jonudell.net/2007/05/24/restful-web-services/ so apparently it's in the book.

Comment on Re: RESTful transactions (a speculation)
by Paul Winkler