I am not sure if they were ever really spelled out in print.
With each tier you do get more space for private messages.
Each tier gets progressively more.
With each you get the ability to have a larger than the normal 100x100 avatar.
You get the ability to start or be invited to join in some of the private forums.
There was supposed to be an @GlockTalk.com email address at some point.
Any pop up adds will be gone from your view.
You get to support a site that actually has operational costs.
An enlightened zeal for the energy and efficiency of government will be stigmatized as the offspring of a temper fond of despotic power and hostile to the principles of liberty.
Alexander Hamilton, author of Federalist No. 1. 10/27/1787