Many websites when ask you to create a new "username", will limit you in some way, most often like "username should only contain letters and underscores" or something alike.
This results in inability to use my email as username and forces me to come up with new unique string all the time.
What is the rationale behind this?
Why not just let users use their emails, as a simple to remember and always unique?
What is generally wrong with having symbols like *&%$#@ as a part of username?