Is it possible to run Mountain Lion on older hardware by using a virtualization solution?
10.7.x or 10.8 (Build 12A269) in VirtualBox

There's an answer under How can I install Mac OS X Lion in VirtualBox, or any other type of virtual machine?.

I guess, a .vdi of Mountain Lion produced in that way will be usable with at least some Macs that might not otherwise run the OS. 

Example

Physical machine: 


MacBookPro5,2 with 8 GB memory
VirtualBox 4.2.0 Beta 1.


In the VirtualBoxVM: 


Build 12A269 of OS X 10.8 
without FileVault 2
with Core Storage encryption of something other than the startup volume
dynamic_pager disabled: 




Alongside an answer to Why would I disable swap file in Mac OS X?, note that without swap files, Activity Monitor measures both: 


virtual memory size
page ins.