Discussion of GTA Online was beginning to overwhelm the GTA V thread, so here's a new one just for GTA Online, as it seems to be a bit of a different beast.
GWJ Crew on Social Club - pm TheHipGamer for an invite.
Rockstar's Support Twitter
Rockstar Launch Support Page
- Back button on xBox accesses the Quick Interaction menu, which allows a number of things including passive mode, request a new personal vehicle, change voice chat options and Quick GPS to your nearest gun store, clothes shop or objective.
- Down on the D-Pad once shows all players on your server. Down twice zooms your mini-map out.
I'll edit the top post with more stuff as users find it.