IIRC, Jin started working for Paik because he married his daughter, and got into the shady-business end of the company because of the debt Sun incurred paying of his extortionist mother. This timeline seems to suggest that they met while he was working directly for Paik and running his shadowy errands. What would his motivation have been without being married to Sun?

Well she's just enjoying the romantic and forbidden affair - she has not had the depressing mundane reality to make her bored and seek out another man for English lessons and illicit fornication. "Sun's bascially a big skank no matter what timeline she is in" is, I think, the intended message.

What I wonder is if HE is 108 on the lighthouse dial? Or is Widmore? Or is Widmore the "They are coming" Jacob referred to with his last words? Is Widmore up to something that both SmokeLocke and Jacob are opposed to for their own reasons, and Jacob was trying to warn SmokeLocke about?

He's got leverage against him - Sun & Ji Yeon. Sawyer & Sayid are too slippery and desperate and unattached, and fairly well stripped of emotional handles. They've each lost the loves of their lives, have unpleasant and criminal pasts to deal with and don't seem to have any means as obviously usable for manipulating them as a wife and a daughter they have never seen (aside from Clementine whom Sawyer voluntarily abandoned).

I suspect it's an excuse for the Lost writers to prolong the conflict with more character dramatics and face-offs, rather than a simple fight-for-the-plane-and-run scenario.

I don't know. It might be that his little three-year interlude with Penny is his happy-time. A respite, if you will, before having to plunge back into Island-stuff for the rest of his life (however short that may be). I'm kind of "meh" on Desmond. He is not that sympathetic a character, seeming to me to be a slightly less destructive male version of Kate - spending his whole life running from anything he tries and sabotaging his own chances for happiness or a good life. He could have made a monk or a soldier or adventuring dude, or even been a kept man with Penny, if he didn't keep screwing things up on his own volition. Maybe Charles saw this in him and THAT was what he was referring to when he said that Desmond wasn't worthy of Penny.