You are offering a free domain with a 2 year subscription. My question is that your system allows for registration of various extensions, including expensive .WS or .BZ that cost about $30. Essentially 2 years of hosting will cost $46.80 (minus fees) and with that you are giving away $30 for domain registration. You are left with $15 over 24 months of service and support at $0.62/month.
I was wondering if any extension is valid with the promotion. If not, and you only offer free .COM/NET/ORG domains, then perhaps you can protect yourself by placing a note somewhere. I couldn't locate anything related to that.