Keep domains in print should be readable by human beings!
When you use your domain name in print, humans are going to have to read and understand it. Capitalization is your friend for printing media since your web address (a.k.a. your domain name) is not case sensitive. If people type it in the address bar capitalized or not, it will site go to your website.
Use capitalization to distinguish one word from the next when printing business cards, brochures, catalogs.