I have been wanting to follow up on various very good blogs posts I've been reading lately around architecture concerns with Saas/mashups. A lot of people bring up concerns on security, etc. when talking about Ajax and the new mashup technology - but old schoolers will say the song remains the same. Sure, there are some new exposure points and those need to be protected, but you primarily need to practice the same good core architecture when dealing in this area.
I fully agree with Robert's comments on reliability and other -ility management for SaaS/mashups as core architecture principles. I think his experience is an interesting case study from a couple of standpoints - one is that presentation tier/mashup developers obviously need to think about graceful error handling in the UI layer in a new way (not sure if that's being done generally), as well as logging and outage reporting (highly doubt that's being done fromt clients as it's not as easy as server-side). What is the common Saas model for this? Does a mashup developer need to setup his/her own monitors for consumed services? Subscribe to an announcement list? Somehow report from the affected clients?