It does work parkdale, but it perhaps wasn't explained fully. If you put in an existing name (eg 'parkdale' or 'factor30') it goes to your/my profile, showing the name already exists.
If you then put in a new name that you'd like (e.g. 'neverbeenused') it will either:
(a) take you to the profile page of whoever already has that name or
(b) bring you back to the opening page, which confirms the chosen name isn't already in use.