My Stanford Encyclopedia of Philosophy entry on Computation in Physical Systems has just been published. As some of you know, it discusses three main topics: (i) what it takes for a physical system to implement a computation, (ii) whether every physical system implements computations, and (iii) which functions are physically computable.
The SEP editors made me work pretty hard on it, but I think it was worth it. I am not aware of any other review of this literature of comparable scope and detail. I hope it will be a helpful resource.
Given that SEP entries are revised and updated by their authors at regular intervals, I hope you will let me know if you find mistakes or additional material I should include in future editions of the entry. (Thogh as always, I may or may not agree that something is a mistake or that something deserves to be included.)