They NEVER talked beyond life-or-death missions, so I think by spending more time together they find they have shared interests. Shikamaru is encouraged to continue to work hard, and Sakura is encouraged to stop and look at the clouds every now and then. Shit happens. They realize that this feels more RIGHT than they thought.

Well put. Exactly my thoughts.

Flirting and foreplay?... See, once you start reading for pairings rather than development and the interaction, you say dumb shit like that. I NEVER got the impression that their arguments were flirty. Ron could say some hurtful shit and be unapologetic about it for the longest. Hermione didn't hurt anyone that didn't deserve it, like Malfoy's nose.