Jamie Cansdale announced that he's coming out with a pro and enterprise commercial versions of TestDriven.NET (yes- it costs money now). Read the full thing here, but to answer the most important question for a lot of folks out there he says:
"Just because the commercial versions now exist doesn't mean I'm turning my back on hobbyist users. There is still a TestDriven.NET personal version available. This version isn't crippled, it doesn't nag you and you don't need to enter a licence code. I could hardly call it "zero friction" if it did."