What's the catch? I'm not sure yet. But here's what I did, and I bet you could do it too:
- I called (866) 921-8086 (as indicated in the email) and told them I was offered a free domain registration for a year. They asked for a promotion code, and I told them my email didn't contain one.
- I selected a domain name, and declined all additional services. They requested a credit card, but didn't bill anything.
- I logged in, and set up a CNAME record, for *.cheaphack.net pointing to blogger (per the blogger.com instructions).
- After that, I had to call tech support (888) 734-4783 to get them to disable auto-renew. Once auto-renew was disabled, I deleted my credit card number from my account.