Let me just say that, contrary to Paul's description of my position may sound to others, I am not blindly "pro-cloud". In fact, I firmly recommend that existing enterprise data centers and applications think hard before going "outside" to a commercial capacity-on-demand provider. In most cases, it would actually be better for such enterprises to convert their own infrastructure to a utility computing model first, while the necessary technologies and businesses mature.
I also define the cloud broadly, to include SaaS, PaaS (e.g. force.com) and HaaS (e.g. Amazon, Mosso, etc.). SaaS is in clearly in play today, HaaS is being experimented with, but PaaS may be the most interesting facet of the cloud in the long term.
That being said, Paul provides very valuable information in this post, and I for one very much appreciate the work put onto it. It is very true that bandwidth is something to be nervous about (especially when Amazon charges as much as it does for bandwidth), and I have had some interesting discussions (such as the one Paul references) about how data integration will happen over the cloud. Finally, cloud-lockin is indeed something to be concerned about; as in, what happens if my first choice provider sucks? Can I move my applications, data, etc. to someone else cheaply enough that it doesn't put me out of business? Simon Wardley has a good post on that today.
Update: Er, two seconds and I could have confirmed the spelling of Paul's last name. Sorry, Paul!