I was fortunate enough to finish the story before online released. So the temptation simply wasn't there. Even if it was though, i'd still finish the story. Its easily one of the most skillfully told narratives i've ever experienced, if not the most. I've never seen a story weaved together and completed quite like this. Incredible.
Also, its definitely in people's best interest to finish the single player story line BEFORE going into multiplayer, that way, the order in which things are exposed to you as a player are succinct and make sense. For those not new to the RDR universe, its one hell of a ride. Will be hard to top for quite some time.