Guests:
-Have to put up with the side ads.
-Can't view attachments (attached within the posts, but are able to view photos in the forum's Gallery)
Members with < 25 posts:
-Side ads disappear
-You get to post an introduction (basically you can post messages in most of the forum's sections)!
Members with >= 25 posts:
-Ability to edit their profile
-Crew Lounge access
-Ability to participate in the trading post
-Can upload to the gallery
-Ability to up-vote posts (give respect points)