The support article addresses a fairly widespread problem where setup stops responding and displays the dreaded "beach ball" after one creates a user account. If you're experiencing the problem, Apple recommends you either wait about 30 minutes for setup to resume, or complete Setup Assistant without connecting to the internet. From Apple:
If your MacBook stops responding and shows a spinning wheel after you create a user account in Setup Assistant, simply allow setup to continue. The setup process will resume after about 30 minutes.You can avoid this delay if you complete Setup Assistant without connecting to the Internet. When Setup Assistant prompts you to select your Wi-Fi network, click Continue without selecting a network. If you have an Ethernet adapter, disconnect it before you start the setup process. After you complete Setup Assistant, restart your Mac. Now you can join your Wi-Fi network or connect your Ethernet adaptor, as well as set up iCloud.
While the support article only addresses the new MacBook specifically, it's logical to assume that the same process can be applied to any Mac that stops responding during setup.
Source: Apple; Via: Glenn Fleishman (Twitter)
