Could we assemble a list of hosting services that use Virtualmin, along with a discussion on how they integrate VM into their system, and problems they have with VM, along with solutions that were found? I'll start with my hosting service, Joyent:
Joyent uses VM in two ways: 1 - Their shared hosting uses VMPro, customized to provide the services they want to give to their shared hosting customers. They are oriented toward not only web sites and mail lists, but also programming with good support for Ruby/Rails, Python/Django, SVN and a host of other services. These are all managed by the hosting user via the VM front end.
2 - Their dedicated hosting service provides a simpler VM GPL front end, assuming dedicated clients may want to use their own administration, via ssh and the Solaris administration tools. They DO, however, offer an upgrade path where you can buy a VMPro license, and they will use that to set up a VMPro front end to the dedicated system. The goal is to have the power of a dedicated, root accessible system, but with the ease of use of VMPro.
We're new at this, but when working with the Joyent and Virtualman teams (who work well together, BTW), our project ran into a problem with mailman installation and VM use. The teams worked out the problems and a fix is in the works if not already solved. A plus for both Joyent and VM is that Joyent has now created a pkgadd for mailman which was not available in other Solaris repositories (Blastwave, Coolstack).
So, any one else want to chime in? It would be interesting to hear about moving from one VM hosting service to another as well .. how well the backup/restore works and solutions for problems.