Raised Floor versus Solid Floor

There is an emerging trend away from raised floor in many large scale data centers. The cost of build out and maintenance for raised floor is driving many organizations to a solid floor data center environment.
Most data center equipment is now cooled from front to back, so cooling from the bottom is no longer needed. A number of different hot spot management techniques can be employed to solve the problem of density related heat.
What's your opinion of raised floor? We'd love to hear about it.