Just going by the 7.5 changelog:
Quote
Spaces will now be removed from the beginning and end of Login Names, Display Names and Passwords.

If the way it is now is the way it is going to be. It would be nice to have a descriptor when registering. So at least there is a warning before you submit.

It is a bigger pain to go back and re-enter stuff like captcha, password and name is used already and keep trying till you succeed.

And as to PDN and user name. My observation is most people use the same name but now you can't.

So my opinion is make both fields have the same entry requirements.
It will save aggravation for the user trying to remember,"Did I use a space or did I use a underscore"

My 2c

Blue Man Group
There is no such thing as stupid questions. Just stupid answers