On Steam, my profile is the following:
Notice the numbers at the tail end of the URL. While other users also have numbers for a profile like mine, I've seen many others users with their usernames in their profile instead. It makes it a lot easier to link and remember your profile page based on a short username instead of a couple dozen integers.
Why do some users have a username in their profile instead of numbers and vice versa? Is there a way to change this?
I originally thought it was based on the age of the account since I was a pretty early adopter back on January 24, 2004, but I've seen new and old accounts with numbers and usernames.
Update: I've since updated my profile URL so clicking the above link will renavigate to the following: