ERP Application Service Providers

During Tet Holiday, I have time to read the Friedman's Book "The World Is Flat: A Brief History of the Twenty-first Century " that is given to me by a friend. One chaper of the book mention about Salesforce, a company that provides CRM software as service via Internet at very low cost. (Software as a Service) SaaS is not new, the idea rooted from 60, 70 year of last century under different name such as service bureau, utilities computing, etc. I think, using ERP as service is very attractive for small, mid-size companies. Searching on Google, I found the following companies (ASP) offering ERP sofware as service 24SevenOffice NetSuite SalesForce TwinField Oracle CRM On Demand RightNow Technologies Fee of service is different from company to company ranging from 40 to 100 USD per user per month.