As the previous post mentioned, in vSphere 5, Guest Operations API functionality that was previously only available via the VIX API has been incorporated into the core vSphere SDKs.
For a cool demo of this functionality, check out William Lam's recent post on his VirtuallyGhetto blog! William created a Perl-based command-line interface to most of the guest operations functionality.
We've found that most people use the VIX API with vSphere for Guest Operations functionality — things like copying files in out of the guest, and running programs in the guest.
With the launch of vSphere 5, this functionality will now be available in the core vSphere APIs, via the GuestOperationsManager object and associated sub-managers.
The APIs incorporating this functionality will be:
Please try them out, and let us know how you like them on the VIX API discussion forum.