PaaS, IaaS, SaaS and now DaaS

Salesforce.com will be adding DaaS to the already overcrowded 4 letter acronyms for everything that is offered in the Cloud. With Database.com in place Salesforce.com will be in direct competition with Microsoft, Amazon, Google and others. What is very interesting is the per transaction pricing. OK, it is not relational DB (Sorry, my mistake, it is indeed relational ) but can it compete with relational data? Interesting questions,
How these vendors are going to divide up the market?
How Microsoft,Amazon and others are going to respond?
Need to consider though that Salesforce.com has been in this business for a while.Price war may be in the offing.