You need to be aware of a few things if you are deploying System Center Virtual Machine Manager (SCVMM) 2008 R2 at the moment.
First thing is that VMM 2012 is just around the corner. The public beta launched yesterday. It brings about some big changes. If you are buying that license then I recommend that you tack on some Software Assurance to get the upgrade to SCVMM 2012 when it is released as RTM.
Next up is SQL Server support. SQL Express has been supported up to now. That limits you to an on-board 4GB database. That’s not been an issue for most Hyper-V deployments. The free license (as opposed to SQL Server Standard edition) was a real money saver and an “obvious” decision – one which I have made myself.
VMM 2012 will not support SQL Express. You will need SQL Server 2008 R2 Standard (or higher edition). Yup; you will have to spend that little bit more. If you are doing the upgrade (after VMM 2012 RTM) then you can probably install SQL Server 2008 R2, detach the database from Express, and reattach the database in SQL Server 2008 R2 (to be verified).
An interesting scenario will be that VMM 2012 can be made highly available. Some have deployed VMM as a HA VM (which I strongly dislike) to get this effect. HA VMM will require a clustered file share (for the library) and HA SQL (for the VMM database).
So keep all that in mind if you are deploying VMM 2008 R2 now.