Say I own domain abc.com.
I think it's a bad idea to use firstname.lastname@example.org as the registrant's (myself) email address. This will cause problems when I need to transfer the domain to another registrar e.g. GoDaddy. The new registrar will then try to send email to email@example.com which is unlikely to function normally since the DNS settings are undergoing changes.
So I believe it's best to use email address independent from the domains I own as the registrant's email address. (Isn't it the practice Google Apps is using?)
Have I missed something here or am I right?