what we don't know about private cloud

This is not one market, it's a hundred (or hundreds of) markets. There is no real big pattern to where the inflection points are. There are lots of little patterns.

We do not know:

• The line between what applications we will run and what we will totally outsource to SaaS
• The lines between what we will leave bare metal, what we will virtualize and what we will actually run in any cloud
• The line between what we will do on a public cloud and in a private cloud
• The degree, magnitude, and timescale of how "virtual private cloud" and "hosted private cloud" moves those lines
• The degree, magnitude, and timescale of how various approaches to cloudifying "legacy" apps via encapsulation, migration, replicating, etc., moves those lines

These lines are being drawn in different places by everyone--including similar orgs by sector or size or whatever and also by different groups within the same org.

Add to that the range of things that are called "private cloud"--everything from "I have a data center with some servers in it" to "I've built my own EC2, EBS, S3, ELB, SQS, and SNS with open source software on commodity hardware and can automate ALL THE THINGS".

Here's something I do know: any number put forth for private cloud market size, growth, or spend is utterly daft.