Vendors are changing their license stance in relation to the rise of virtualization. Even MS has got into the act back in January. They relaxed the "on install" stance - meaning you couldn't even clone an install of their products - and now are stipulating their per processor licensing can be split up between virtual servers and you can have as many domant copies as you want. Their most recent release of their OS (Windows Enterprise Release 2) goes even farther is licensed to be run at upto four instances as once regardless of processor.

Below is from an email I sent trying to clairify this with one of the committes.

FYI - Speaking strictly as to Microsoft products, there was a change last year to open up their license model. You may now:
  • Have as many copies as you desire (non-running installations)
  • Run based on the number of Virtual CPUs, not physical CPU
Using SQL Server as an example, if you have a two-processor license you can; A) run a single instance on one two-processor box, or B) run two instances on two single-processor boxes.

Attached is The MS Brief.