Pair launched four days ago. Since then, the Y Combinator company has racked up 50,000 users, Greg reports from YC’s Demo Day.

Not bad. Its impressiveness is only slightly diminished, when you realize that that stat is not by couple: Half of those users are the ladies who’ve convinced their boyfriends to join.

Not that Pair, for all its cuteness, should be written off as a lady thing. A private sharing portal for the types of people who probably share the most information — couples — is an awesomely smart idea. And I’m not just saying that because I’m a female who likes cute things.

I see it as a utility considering that, at the moment, I use too many channels to communicate with my boyfriend. I’ll text, “Did you see my email?” or send an IM telling him to play his turn in Draw Something already. He’ll email to ask if I got the song he sent me in Spotify, drop links onto my Facebook page, or text me photos he also uploaded to Instagram. Sometimes we are conversing via text, playing Words with Friends, and sharing links to stories over email all at the same time. It’s a little much.

Putting it all in one place is a great idea.

In a way, it reminds me of the HowAboutWe Couples product that I wrote about a month ago. The dating site, which focuses on date activities over “perfect match” type algorithms, launched a couples app that helps pairs come up with date ideas, communicate, and in some cases, buy them.

Pair takes that idea and applies it to sharing, the scrapbooking part of the relationship, if you will. HowAboutWe Couples is focused on a single utility — making plans — and is just another place to look for a potential message from the old ball and chain. Pair is more about communication and sharing. Given the choice, I would probably use Pair.*

But the appeal is for big sharers like my boyfriend and I, and probably not for couples who live together or see each other every day. Plenty of married couples I know, even young ones, use a shared Facebook page and email address. (I’m serious… Think “thesmiths@gmail.com”.) Really close ones like those, or really any couple that lives together, probably do not need an app to share.

The other questions I have for Pair: What do they do when couples break up? Do their Pair-paths live on as a bitter reminder? Can they delete them? Can they start new relationships? What if they get back together?

HowAboutWe kills it in that regard because they are, at heart, a dating site. When a HowAboutWe couple breaks up — boom, “Why don’t you get back out there by signing up for HowAboutWe, a brand you already know and love?” Based on its name alone, Pair is kind of stuck with the focus on, well, pairs. There’s already an app for what Pair does for singles, it’s called Path.

And secondly, what is their policy on sexting? They’re storing this stuff on their servers, and even though Pair’s goal is certainly to be lovingly cute and not raunchy, no possible set of users could be more ripe to turn a service into a porn pit.

Other social networks like Facebook, now Tumblr, and, famously, Google+, have policies against objectionable material posted on their sites and actively police their sites to keep them clean. But if Pair is trying to replace the normal private channels couples use to communicate — texts, emails, IMs, Facebook, Spotify, Instagram — shouldn’t it allow all types of such communications happen? Seems potentially like a legal mess, particularly when the aforementioned breakups occur.

Greg is still at Demo Day. We’ll update if he gets a chance to ask Pair’s founders about either of those questions.

*Given the option, because Pair is not yet on Android.