Currently users are instructed "(If you don't have your own domain name, we can provide you with a subdomain of ambitiouslemon.com (e.g. niftysoft.ambitouslemon.com). If you want a subdomain enter it (e.g. niftysoft) in this field.)" beside the domain name text entry field.
People tend to have a lot of problems with this for some reason. Our most common problem with new accounts is that their website does not resolve because they either got confused by this instruction and entered their domain name incorrectly or they do not own the domain they listed and thought we would buy it for them.
A pull down menu in which users first select whether they have their own domain name already or whether they want a subdomain of ambitiouslemon.com which then provides a text entry field specifically for that option could help alleviate some confusion.