Somehow I missed the announcement that SP1 was released for Virtual Server 2005 R2.  Given that I run nearly all my development (and some non-development) environments on R2, I'm surprised I didn't catch wind of SP1!

You can download SP1 here: http://www.microsoft.com/downloads/details.aspx?FamilyId=BC49C7C8-4840-4E67-8DC4-1E6E218ACCE4&displaylang=en.  It's interesting to note that Vista flavors are listed as supported host operating systems, yet include a "non-Production only" caveat.

I run Virtual Server 2005 R2 on Vista Business without any problems (well, if you know some tricks).  As I upgraded I noted the following:

• When installing SP1, be sure to turn off the Virtual Server service, else you will receive the following warning:

• It will detect the previous version and force you to upgrade:

• I could be wrong, but I'm pretty sure that some of these options are new.  Sorry, I haven't had the time to research them - when I do, I promise I'll post my findings.

The upgrade seemed to go without a problem.  I was able to mount and start my virtual machines without any problems whatsoever.