Just came across this: http://use.perl.org/~Alias/journal/38036
Commencing this month, Microsoft will be providing every CPAN author with free access to a centrally-hosted virtual machine environment containing every major version of Windows.
The result is now practically the entire Perl community has a zero-cost and zero-setup way to doing light development, problem replication, debugging, and ad-hoc hesting on every version of Windows.
This arrangement is particularly amazing because it is, to my knowledge, several orders of magnitude larger than anything of this nature ever attempted before with the Open Source community.
(Also posted @ /.