It's nice to hear, every once in a while, that you're doing something right. It was happy happenstance (happynstance?), then that I stumbled on this short essay at Gamasutra this past week. In this piece, the author describes a few case studies of applying usability testing to game development and the benefits seen via those tests.
The article can be boiled down (in a similar fashion to the article I looked at last week) to essentially "usability testing is good," which is a reductionist but perhaps necessary message for the game development community. It's nice to hear that validation, then, given the past focus we've taken in the lab on usability.
It wouldn't be fair, though, to say that our testing has taken place in an environment that may be directly translatable to a real game studio, given such issues as scale and budget. One of the best pieces of information I think I can draw from this article is the template provided for adapting usability testing to an agile environment - the idea of layering UX testing onto the end of a feature and minimizing the overhead of waiting for UX testing to finish by moving on to another discrete feature in the interim.
The article is also well-served by including a number of beneficial examples, but they simply serve to underscore (rather than elaborate upon) the original point ("usability testing is good"). The second-best part of the article likely comes from the comments and not the article itself, where an astute commenter makes note of the cost-to-implement versus time relationship - the primary selling point of usability testing in the event someone balks at spending additional money up-front.