Not sure how this one slipped past me, but 10gen announced support for the Ruby language and most of the Rails framework APIs on their open-source cloud service last month.
This addition is great news for 10gen and for cloud computing (the hosted-application-platform flavor, not the hosted-hardware/datacenter flavor).
For 10gen, support for a well-known API and app model is a huge bonus, which makes it easy for people to move an app into the cloud without learning and coding to new APIs, and also lowers the perceived "lock-in" involved, should the move not work out.
10gen takes a big step forward, joining Stax, Heroku, and morph labs in supporting Ruby on Rails in the cloud.
Of course, the language is only half of the battle -- there are the APIs to deal with as well, and issues will typically arise where the impedance mismatch is highest with cloud-related infrastructure. E.g., cloud databases are mostly non-relational and don't support SQL ... so an ActiveRecord or SQLAlchemy API won't work on 10gen's 'grid database' (a reasonable tradeoff for simpler scalability.)
Even so, it is starting to appear as though one could write a lot of core business logic using, say, Python, and expect it to run unmodified on most vendors' clouds. Not a bad position to be in for the Python folks.