On the contrary, for a great many sites (low impact) I'm happy that they finally figured out to use my email address as a username. As a usability feature, it's much nicer than having to guess at whether my standard usernames are taken.
There are many problems with this. Among them that I have some iTunes purchases associated with an email account that hasn't existed in /years/. There's no way to rename an Apple account. This same problem exists on most sites that use email as username - if your email address of choice ever changes, you're SOL on having a single identity anymore.
Not only that, but I have my own domain name which forwards anything@mydomain.com to my primary email. And to keep spam under control, I use a unique email for each (low impact) service. Therefore, I often forget which email I used when signing up for that particular service (unless they sent me a conformation mail, then I can usually dig it up).
