We can change our username link..
For example..
From -> http://www.facebook.com/profile.php?id=1086243667&ref=profile
you can change into this -> http://www.facebook.com/embotrd
Simply you just go to http://www.facebook.com/username and follow the instruction..

First, u might seen this
This is username suggestion from Facebook.. if we want to choose our own username, click "more".
Then, enter your desired username..
For Example like picture below

After done, click "Check Availability"
If there's no one use your username as their username.. It should be available...
Here the picture if your username is available..

Confirm to set your username like you want..
Here the picture if your username is not available..

If the username set completely..
The window will open like this..

That's how to make your own username on Facebook..
Sorry if the image picture so small.. hehe..
Thanks..