So Jude added:
...for what it's worth my take is that it's not necessarily the 'quantity/type' of sex featured in a ModX (though those points that Nat makes are certainly valid and useful) it's the sexy/sassy/young tone and vibe. In essence it's character over the physical act - i.e. today's Mod X readers want to read about the woman they aspire to be so let that be your guide. Kelly Hunter's debut wasn't sex filled and the heroine was a virgin but what developed was 'totally aspirational sensuality' for today's young woman. I know I've read Mod Xs across the gamut of 'degrees of sex' so I don't think there's a barometer on it. It's about attitude and convincing, real characters. I.e. the kind of thing we want in a good book anyway, it just so happens that these books have a particularly young fresh voice - but never fluffy or whimsical. I would tend to say - go with what you're comfortable with and focus on your characters/storyline/voice being the essential 'traits' of a Mod X.
And quite right she is too - esp re the comfort factor there isn't a barometer - you have to write what you feel comfortable with and some MXs are more explicit than others. And if you try to write something you're really not comfortable with it will come across and won't work. Ultimately it does depend on your characters and the situation you've put them in as to the when/where and how. But it is inevitable.
Thanks for bringing up Kelly's book - because this is one of my all time favourites and Marcy keep an eye out because I believe its coming to the US soon and hopefully that means Canada too. Anyway, I would say that book is a very sexy read - take the beginning plot points - the heroine meets the hero in the first scene - they also kiss in the first scene (twice in fact!) - the sparks are flying from word go and are shown to fly even more in the next couple of scenes - when they're on the airplane she positively torments him! He really struggles to keep his hands off her and vice versa! I don't want to give too much away because you really SHOULD read it Marcy - but they do 'get it on' pretty early in the piece and in fact it is the heroine who drives this - so even though she's a virgin she isn't a shrinking violet and she refuses to miss out on a piece of the hero. It is very sensual and also very funny. I guess yes, not that explicit but I mean, hey there's a discussion of SIZE in there - its not that prim either! ;)
I guess it shows that you don't have to write all the ins and outs but you do still need to have sensual, confident characters. I know for a fact the eds don't want Miss Goody-Two shoes heroines. They want heroines with a bit of gumption who'll go for what they want - whether they should or not...
You can read an excerpt from Wife for a Week on Kelly's website here : http://www.kellyhunter.net/books.html