[tipper]

I'd rather see Sun not pregnant anyway.     Now that you mention it, it will take a good make-up & effects crew to keep these folks looking like they've been there several months, when in fact it will have been several years for the actors to age. 

That's easy for "THE BABY!" but not so easy for "WALT!" or most other actors...

Anyway, I think they have so many story lines to develop, that they can pick and choose which ones to perk up the audience with.  Sun pregnant might be just a short topic.

[yada yada]

I think thats probably the whole point of sun's pregnancy, to add a new mystery to lost on which fans can discuss and put forward their theories on.  It's also an obvious plot to bring sun and jin closer and give them a new element of connection and to keep their storyline in the show alive.

[Peel]

a young, beautiful pregnant woman losing her long awaited love child would make a great dramatic plot... We'll never see her giving birth anyway so I guess she'll never have that baby...