Today, Google anounced the general availability of its Goprogramming language on App Engine. It will be interesting to see how this pans out, but this very well may be the kind of endorsement needed to catapult the language out into the semi-mainstream. While still young, this language is looking very promising.
My initial tinkerings liken it to a cross between Python, C, and a little bit of Java. Visually, it seems to look the most like Python and C, which is a big plus for someone who loves the syntactical minimalism of Python (not so much C).
While there are certainly going to be some issues right out of the gate, it will be very interesting to watch App Engine and Go evolve separately and together.