[dchest]

NN/g are well-known for developing methodologies for usability testing. They promote tests with only a few people, e.g. see http://www.nngroup.com/articles/why-you-only-need-to-test-wi...

[sspiff]

Thanks for the link! That explains their sample size. I don't necessarily agree with using a single tester though, the numbers in this post speak only of averages, which means you can still get a bad seed.