Somewhat related: "Gift guides" is one service that I considered unsolved. Every holiday (Christmas, birthday, father's day, mother's day, etc) I struggle to come up with gifts for the people I care about. In many ways it's demoralizing. If I care so much about someone, why can't I think of a good gift for them?
There are lots of factors here, but I think it basically boils down to, as adults we generally get what we need/want during the course of the year. So gift giving is really the art of giving things people hadn't thought of, but still would like. That's a tall order!
In recent years I've tried searching for "experience" gifts, which I believe to have more value. Nights out to exciting dinners, fun shows, events, etc. But the sites that serve those needs (Groupon et. al) are really rather scummy. All the businesses on there tend to be poorly reviewed; just using those sites to push polished turds of a deal.
I look all the time for gift guides and helpful sites and always come up empty handed. The lists on Amazon mainly push Amazon's products, which are garbage, or really common/useless stuff (there's no-one in my life who needs a kitchen stand mixer; they all already have one). I've read idea threads on Reddit, and those mostly boil down to "Man, all I want for Christmas is a pair of shoes. I'm really poor." followed up by a bunch of helpful Redditors. Not that that is a bad thing, but it's useless as a gift recommendation.
Before the deluge of rhetoric replies: yes, rampant consumerism, corporate marketing holidays, donate in someone's name, etc, etc. I happen to enjoy giving gifts, and would love to give more meaningful, personalized gifts (like those experience gifts I mention). I'm just really bad at it. And regardless of that rhetoric, can you honestly tell me that you would pass up an opportunity to build a successful "gift guide" service? I can't even imagine how lucrative something like that would end up being.