Last year when interfacing with several Web services for a project I found Tammer Saleh's "Coding for Failure" indispensable. Although it was presented two years ago, it's far from out of date.
You can check it out on the Confreaks website and download the slides from here (the link on Tammer's website is broken).
Specifically I found Tammer's summary of different exceptions helpful which I have included here:
See slides for handling in controllers and rake tasks and notification using HopToad.
