A Unity ID allows you to buy and/or subscribe to Unity products and services, shop in the Asset Store and participate in the Unity community.
Separate names with a comma.
I gave this a try this morning, and can report that with the v3 beta, the problem does not occur; after I quit Unity, the Unity Hub still displays...
Perhaps this is working as intended, but it seems weird to me: 1. Launch Unity Hub 2. Click on a project to open in it Unity 3. Quit Unity 4....