UPDATE: The Title Update also fixed the following issues too.
Fix for interface issues when using Internet on the cell phone after completing the game, or during a mission replay
Fix for the Vanilla Unicorn occasionally becoming locked
Fix for issues where the character’s money could drop below zero and become stuck there
Fix for the Epsilon Program missions not progressing properly after delivering some cars
Fix for issue where the Atomic Blimp sometimes does not appear as a phone contact for Collector’s Edition owners
Fix for issues with saved vehicles going missing, or losing their upgrades
Fixes for several map escape and collision issues along with other various bug fixes
GTA Online is a go! It's being switched on all over the world gradually and you will know if you have it as you will prompted for a title update/patch when you start your game next. Have you tried it? Is there any issues you've experienced? It's obvious that small problems will be encountered at the start as R* work on getting the server level up to what's needed, as this section of the game is something MANY have been waiting for!