It won't let me register an e-mail address with a + sign in it. I prefer customizing my gmail address when I enter it on a random site like so: username+sitethatmightspamme@gmail.com
Unfortunately this site tried to be clever, so I had to use one of the alternative domains. I don't understand the thought process behind blocking mailinator. It must surely be better to have a potential customer, than blocking them because they don't use a "real" mailaddress?