To install on the Windows 8 PC, I used a product key given to me by Microsoft for pre-release testing, otherwise you would have to go to Office.com to buy a subscription and get a product key. (A free 30-day trial is available.) The Windows 8 PC install took about 20 minutes, and a helpful introduction walked me through key pointsof Office 365.
Nonetheless, the interest among developers was very strong for a product introduction and was only 4 points shy of the interest in the iPad when it was introduced.