The parallel lives / alternate reality / coexisting universes / prime number / cannot upset the equation concept should be expanded upon in tonight's ep ... and I expect we'll see Hurley win his lotto jackpot with the other set of numbers. The prime this time is 53
post-viewing update: Well, despite the still image floating around with the different set of winning lotto numbers, we didn't yet see that scene and we got no Hurley's dad (boo-hoo) and just the one scene (previewed often) with his mom in the ep Everybody Loves Hugo. Sideplot took away a bit of the mystery when Michael appeared to Hurley at Libby's grave and later revealed that he was trapped on the island, as are many others - strengthening the purgatory aspects of the island vis-a-vis the good vs. evil component of the story.
We got the two Hugo realities and the two Desmond realities, and as with Charlie, the Alt+B timeline (as I'm calling it) that the LOST writers are focusing on as they close the show seems to be where our characters get glimpses into the island reality that has made up most of the show. They seem to be dispensing with all but two timelines.
Desmond has seen, and he is now hell-bent on changing outcomes.
He served an almost Jacob-like role in the Alt+B timeline getting Hurley to pursue Libby and have that date on the beach that never happened on the island ... mission accomplished (Hurley kissed and sparks really flew - he saw the other reality - the post-crash island - in flashes and the rich golden color-saturation) ... kudos to actor Jorge Garcia - it is always a mark of a fine actor when they can just silently react to something and convey deep emotion or move a scene along. Garcia was just terrific, as was actress Cynthia Watros - who played Libby in three touching scenes.
Desmond even staked out John Locke and ran him over ... and back on the island MIB/Smokemonster/Locke threw that Desmond down a well (despite knowing Desmond has some special magnetic properties, as did the well) yet Desmond is completely content with whatever happens to him on the island.
I'm pretty convinced that the EM field Widmore subjected Desmond to with his machine either lets Desmond transcend both realities simultaneously or he saw enough to know that what he does in the back-on-the-mainland reality is much more important than what he does on the island. I suspect we'll get a flashback at some point showing us Desmond's POV of that moment in the EM field. Despite Eloise's admonition not to "break rules" he is breaking every rule he can to upset the balance.
If Eloise is determinism then Desmond is the bringer of chaos.