Big news! You can now join the site using the Facebook Connect button. This is as simple as clicking the button and then clicking "Allow". No registration is required. Then, you will be able to always sign in by using the Facebook connect, if you need to sign in at all.
If you are not already a GUS member, at the top right of your screen you will see a login status that reads "create account or sign in." Click "create account" and a window will appear which contains the Facebook Connect option on the right. Click that button and then click "Allow" when the window appears (you must already be signed into your FB account for this to work but everybody always is aren't they?)
Also, if you are already a GUS member you can connect your FB account with your Wikidot/Ground Up Strength account. To do this, while already signed in to GUS with your regular username and password, go to "My Account" at the top right of the page, click on "Settings" and then "Connect with Facebook." Easy Peasy.
Edit* If you are not a member, instead of seeing the 'creat account' link you will see a "Join GUS!" box to the left of the 'sign in' link. Click that to join (register OR use FB Connect).