Since I joined in in the status bar, I figure I'll add my two cents to the thread, too. While breasting boobily along, because ahahaha, I'm still laughing at that. *coughs* Sorry, totally serious here. My two cents are really not worth much.

I've only ever seen this popping up in the 1x1s and have heard about it happening during a D&D campaign start, but usually I don't wind up writing with those people because, following their rules, I can't or I don't like their plots. I've been a bit disappointed on occasion, but I never really thought much on the subject because there's lots more fish in the sea. But reading all the posts and arguments, I have to agree that, generally speaking, it's not the best way to make a good impression or gain the best results. As Sierra said though, it's their choice, and it has some consequences. Like most choices.

Most of the time, I'd say it's silly and not at all openminded, however, I [i]have[/i] heard instances of trouble with other writers who couldn't separate themselves from their characters and became horribly possessive and stalkerish of their partner and their partner's character whether their partner wanted them to be or not. I've also heard of spouses and significant others having a hissy fit about their loved one writing romances with people of the opposite or same gender. In these instances, I could understand why someone might try to limit their interactions, and why they might be upset about someone lying to them. Even if they've been having a blast prior to learning the gender of their partner.

Granted, the first would be generalizing from one or two (maybe more, I dunno, though I'd say go whoever's persevering) bad experiences, but those can severely ruin any chance of fun someone might have had and they could be hoping to avoid that in the future. And the second is probably suggestive of a need to get out of that relationship (or communicate a whole lot more), but that's not an easy thing to do. 

Those are the two instances I can think of where I would say yes, okay, fair enough. But I'm certainly not going to ask them to justify their choice if those are reasons I think are valid. I'll simply hope they have better luck and eventually grow brave enough, or their situation changes, to give them the chance to branch out. I'm not sure it would solve their problems either, but it's an attempt I can understand making.

I have no way of knowing how these people guarantee that their partners are of the requested gender, and maybe it's enough that they feel they can trust them to have read and followed the rules. And for that reason I do think it's a bit of a darker area to be lying about your gender, even if it's by omission, unless you know why the person wants the specified gender. Though I still don't think lying is the best solution to that problem, I also don't think it's hurting anyone, if it is just that they prefer one gender over another. I've been tempted to do the same myself sometimes. If I saw a plot I really really wanted to play, but couldn't, I'd probably just borrow it and see if I can find someone else whose preferences I do satisfy who wants to give it a go with me.

But, I also don't often write romances, I'm apparently horrible at it. Even if I love the story idea. Maybe if I wrote them more, I'd have a better understanding of this issue.