In my first game (Mage Jenny*), I found a gift for sale in the beginning of the game, and Alistair loved it. We'd hardly had any interaction, but I could already open a conversation with "Has anyone told you how handsome you are?" When I realized that the gift was essentially a cheat code for romance, I restarted my game, and played through without the extra romance help. In that game, even though I raised his love/hate meter just as high, I never got the flirty conversation option. When the romance started, it was the "I want you to know that I care about you" kind of romance, rather than the "light flirting" kind. Alistair and I went from platonic friends to people who care about each other, to people in love.
In another game (Teryna Jenny), I managed to raise Alistair's opinion through better conversation and gift choices, without having played through much of the story. And in this game, there is flirting. Because he likes me, but doesn't know me. There's no serious "we've been at each other's backs for this long ordeal" yet, but there's affection and attraction, which becomes flirting.
So the way in which I woo Alistair makes a difference. Gaining his affection via doing good in the world and having his back yields different results than gaining his affection via joking and gifts. And that's interesting.
(For the record, with Teryna Jenny, I tried the "sleep with Alistair" conversation option as soon as it appeared, to see what would happen. He said no. He's not ready.)
*I got tired of coming up with good/clever/world-appropriate/etc names for characters, so now every character I play is named Jenny. Male or female, sci-fi or fantasy, human or not. So I have Mage Jenny and Dwarf Jenny and Teryna Jenny (and a few other Jennys I abandoned immediately when I realized I'd made a mistake in the character creation).