We've had several stories fall on #2 and #3, so we can certainly agree there. The rest seems like common sense, so we'd agree there too. The ones built around other goals tend to work, but where the "goal" was to get two characters to sleep with each other, the story segments rarely moved beyond that point, always falling on it because of the lack of a proper goal. When romance becomes plot rather than subplot, its very easy for the story to break.

Some such can be fun to write, but in the end, most such end up being fairly pathetic. 

We have no truly great romance subplots we'd like to bring forward, but its still an interesting topic. Not in the least because a proper romance subplot is a very powerful storyteller tool if wielded right. Make or break for the story, really.