Very good post. This is the type of post that keeps me coming back since quite some time.
Sometimes I wonder in all the discussions around web application frameworks be it Python based TG or Rails, etc. whether you are not constantly confronted with integration to packaged applications (like SAP) and infrastructure services like SingleSignOn, Active Directory, Archiving solutions, BPEL engines, MQ, data warehouses and all this enterprise stuff. Yes I know, this is J2EE and .Net territory, but even a smaller web applications might have to interface with quite some of those existing facilities. (and usually they don't provide REST or XML-RPC interfaces).
What's your experience and opinion on this?