There's been some discussion that was started by Kimber An, author of the YA SFR--STAR CAPTAIN'S DAUGHTER--and one of the bloggers at Enduring Romance, on a Romancing the Blog post.
It focuses on the heat level in SFR and why some readers believe less is better. I don't tend to write "sweet" (more along the lines of "steamy") but I thought this topic raised some interesting points for SFR fans.
Romancing the Blog: Why Some Readers Hate Graphic Sex Scenes (by Kimber An)
The Galaxy Express: Will "Sweet" Science Fiction Romance Survive?