It's easy to agree that a monolithic portrayal of anything is bad art. So always portraying sex as embarrassing/awkward/etc. would be a problem. Nicola's experience is as valid as mine, and mine hasn't been too bad either, thank you for asking.
And to quote Le Guin, "[W]e have a bad habit, encouraged by pedants and sophisticates, of considering happiness as something rather stupid. Only pain is intellectual, only evil interesting. This is the treason of the artist: a refusal to admit the banality of evil and the terrible boredom of pain."
But there are other issues here, issues of cultural assumptions and power, that maybe need to be addressed.
If we look at popular portrayals -- film, television, and, let's go there, Harlequin novels -- we do not, in fact, see sex presented as embarrassing or awkward. What we see is typically a monolothic portrayal of sex as ecstatic, mind-blowing, world-changing. (Exceptions do occur on "sexually sophisticated" programs like Sex in the City or The L Word, but they are portrayed as exceptions.)
As we know, there are other areas in which popular culture tends to show monolithic portrayals. Women are skinny and clear-skinned; men are bulked-up and competent with violence; values are Western middle class; Americans are heroes.
The trouble with those portrayals is that they impart the implicit message that this is the way things should be. Women should be skinny, men should be competent with violence, values should be Western middle class. Those who are not, are implicitly told by these messages that they are "wrong," that their difference is a defficiency, that it is their fault.
When popular media consistently portrays sex as ecstatic and mind-blowing, it sends the message to every person whose experience is disappointing, "There's something wrong with you." (Actually, Nicola did it in her blog entry, probably unintentionally: "If it's not that way for you, maybe you're doing it wrong.")
I agree that sex should be wonderful. And food should be plentiful, nutritious and tasty, and people should be able to hold their tempers until they can speak rationally, and parents should be nurturing and kind, and brother should not raise arm against brother, and they should beat their swords into ploughshares and their spears into pruning hooks. But the possibilities for fiction become limited when we portray the world as it should be.
One of the virtues of "sophisticates and pedants," annoying as they are, is that they try to subvert this hegemony of the Normal. They portray class, race, body type, cultural value differently -- and they portray sexuality differently too. The advantage, or supposed advantage, of this sort of portrayal is that it is a remedy to the cultural power of the Normal. They send the message, I hope, that you need not think there is Something Wrong With You if the stars didn't fall from the sky every time you had sex.
I don't think Nicola is arguing for a monolithic portrayal of sex-as-miracle. I think she's right to point out that monolithic portrayal of sex-as-unsatisfying is lousy. She acknowledges that "bad sex" exists. I wanted to complicate the discussion a little.