SaaS presents additional issues to consider. We're in a building phase for SaaS and most of the infrastructure that provides high reliability in other utilities, like the phone system, is still being deployed in SaaS.
One of the most important issues, in my mind, is backup and how well protected you are from experiencing downtime. I think it is unreasonable to think that you will never experience downtime, so you want to ensure that it will be minimal. In my opinion, a vendor that has a fully redundant data center to back up the primary gains points in the evaluation. A vendor that needs to ship backup tapes to another location in the event of a problem is a less desirable choice.
Evaluating and managing your expectations appropriately will be a big help in this era when the SaaS infrastructure is still being built out.
This was first published in March 2008