Edit (3/24/14): A stackexchange employee has confirmed in chat that the site will go public tomorrow or Wednesday.
When public beta starts (hopefully in the next week), several important things will change (feel free to add to the list):
- Privileges: The amount of reputatiom you need for various privileges will change. The biggest change will be voting to close and reopen. This will now require 500 reputation. You can see the list at https://academia.stackexchange.com/help/privileges (a site in public beta).
- Moderators. There will be several new moderators chosen from among users. Their role is to keep the site running smoothly, and to help new users feel welcome among other things.
- New users. The site will be open to all internet traffic and appear in search engines, as well as in other stackexchange sites. This will bring in many more curious people than now.
- Publicity. Each question and answer will have a "share" button. This gives you a personalized link to direct traffic to that question. Sharing our best material is the best advertisment.