Is it really good value for money?
I am now looking after around 50 machines, with XP - we will need to move in the future, but a lot of them will need replacing to run W7 or Vista, so is it really an advantage for the OS, when we will be buying new machines with an OS installed anyway?
Just what advantage does Open Value bring to the operating system side? It is only an "upgrade", so if I buy machines with Vista or Windows 7 installed, I then get the right to upgrade them to Windows Vista or Windows 7... As it is, they will be downgraded to XP at the moment, so it doesn't make much difference in that respect.

We have the requisite number of CALs currently, so that also doesn't seem to make much sense to bring under Open Value at the current time - when the user base expands or we need additional servers, maybe.
We have a mixture of Office, from 2000 through 2007. We need to migrate all users to the same version. That is something that would seem to benefit from moving to Open Value, or similar scheme.
Has anybody had any experience on using one of the MS site licensing schemes? I'm tempted to go for it, with the need to gradually upgrade all of the machines to Office 2007 (2010?) and Windows 7 over the next 3-4 years, but at the moment the OS and CAL side of the equation don't seem to add up.