Ahh threesome fics. Personally I like almost ANY Naruto x girls (except Tsunade and Shizune because they are like family) pairings. Of course NaruSaku is my favorite and adding another girl to the mix is fun (NaruIno is my second fav. crack pairing, so I like NaruSakuIno).
Now NaruSakuIno is always fun to read. Sakura and Ino are both rivals who fought over Sasuke when they were younger. So whys it not fun to read about them being in a love triangle with Naruto when Sasuke doesn't give a damn about either of them? Naruto is seen as a guy who has lots of love to offer, and I can believe him in a certain pairing(s) as long as it is done right and for a legit reason.
And most guys will usually do/read a Naruto/Female/Female pairing because it's appealing to them. Naruto with two hot girls? Hell yeah! They don't want another guy in the mix! (If they don't like yaoi that is, and I'm sure that's all if not the majority)
Now to me I just see this as a gender thing. Boys seeing a guy with two girls is great, but to girls they don't like it. They want an emotional aspect to it instead of a sexual one. But the thing is most guys don't give a damn about the emotional connection. They see two hot girls making out, they are going to stare and drool. Girls are different. They like the emotional bond and connection between the two characters. That's why NaruSasu is so popular because they spin the characters rivalry/brotherly connection into something romantic.
Now I enjoy reading Naruto harem stories but there are things I cannot stand such as turning the females into sex slaves and all of them are bisexual. I see that just as bad as yaoi fangirls who turn every obvious het. character (Kakashi and Iruka) into homosexuals. Mind you, I don't go looking for yuri fics, but if a scene comes while I'm reading a certain story, then I'll read it. But if it's something about the "emotional" connection between the two, then I could care less. Yeah, shoot me, I'm a guy!
And as much as Team 7 are my favorite characters, I just don't see Sasuke as a romantic person. I absolutely cannot stand when authors bash him, but I do understand when he isn't paired up or romanticized because to me that's completely OOC for him.
So yeah threesome fics (M/F/F) are fun to read if they are love triangles and the pairings are done with a good believable reason and plot. All standard rules for a fanfic also apply.
Well, I don't like M/F/M if it has no emotional basis because it's no longer about the character, it's all about the smex appeal. Girls are just as guilty of writing yoai for those reasons, not because the two characters actually have something going for them, it's cause it's hot. It's also sad to think that guys don't care for emotional connections. It gives me a vibe that guys don't really care for how girls feel, they just want them to have them and to see them with each other. I respect guys enough not to think this of them, which is why I'll very rarely read girl x multiple guy fics.
You can like it, there's no problem, but it just doesn't feel like a good
story, and it's one of those things that in my mind makes for a bad fanfiction. Lemons/limes with very little backstory and disregard for the characters make it just that, a lemon. Now it could be just my age, but something like that is a put off, and is too porno like for my tastes. Most girls will love a guy too much to be able to stand him loving anyone else. Guys usually never consider the possibility of 'sharing' the one they love either, whether it be with another girl or guy.
And--Guys have the ability to write good, emotional pairings too. It was a guy who wrote Equinox and the prequals and such, I've seen guys write beautiful, real-life love in the Inuyasha fandom.
And like you said that Sasuke isn't a romantic guy--Sakura is not going share any guy. She's proven that with her rivalry with Ino, Naruto would be no different ESPECIALLY if she was serious about him. I hate the characterization in harems and such. That's a major hate of mine, because throughout the entire thing it's OOC, there's no plot, no anything, that can make it possible. And I don't care if you're a guy or a girl, you come up to me and tell me you've been in a relationship while with me, I'd shoot you down, and then probably go and cry. It must be a girl thing.