Goldman Sachs is nothing if not efficient in the way it goes about finding promising, young start-ups that it might eventually help go public. Why set up individual meetings with each company when you can hobnob with more than 30 of the most talked-about Silicon Valley start-ups at a private Las Vegas conference?

We've got the full list of who went at the bottom.

Let’s pick on a few of these, shall we? I spy at least three on this list that have no business even being in the same sentence with the letters “IPO”—at least not anytime soon.

Instagram. It’s a photo sharing service with $7.5 million in funding. And it has no revenue model whatsoever. As for how it can make money, well, there are a number of ways it could happen: charge for extra features, offer tiered subscriptions, or start an advertising program with big brands. The company claims it has more than 12 million users snapping and sharing pics with each other, which isn’t a bad start. The bolt-on-a-business-model approach can work but it’s a huge task for a company that’s in a very competitive space.

Klout. This one seems especially puzzling considering that Klout’s own clout has suffered a number of blows lately. Influential writers have recently called it “the Internet equivalent of herpes” and “sad, and possibly evil.” Sure, a few advertisers might be willing to experiment and pay for the novelty of finding online influencers now. But in the end, will anyone really care about your Klout score? (Here’s a pretty good argument for why they won’t.)

Quora. Another well-designed novelty. Got a question you need answered? Try asking the Quora community. Sometimes the results are helpful—like when Facebook cofounder Dustin Moskovitz answered the question, “What does Dustin Moskovitz think of “The Social Network?” (It was an interesting portrayal of the truth, in case you were wondering.) But it's not clear that the company has managed to grow its users beyond the tech crowd. The business model? The founders have hinted at advertising but so far they’ve remained just hints.

On the other end of the reality spectrum is Birchbox, a subscription service that sends beautyphiles four to five top shelf cosmetic samples every month for only $10. I met the two young women who dreamt up this ingenious idea when they attended Inc.’s “30 Under 30” event in New York in August. Since launching in September 2010, they’ve managed to grow their subscriber count 40 percent month over month on average. In July they had 45,000 subscribers but say now that number is much higher. Birchbox’s last reported projected revenue for 2011 was more than $7 million. Here's a start-up that has it together.

I’d also identify Airbnb as a no-brainer pick. Along with mobile device payments service Square, which also landed on Goldman Sachs’ roster, it joined the $1 billion valuation club when it raised $112 million in Series B funding in July. Airbnb is growing like crazy because its service—which lets people rent their couches, bedrooms or tree houses, for that matter, to others—is a win-win for everyone involved. Sure, it’s had a few missteps along the way, as most scaling start-ups do, but it works. The hosts make money and the guests save money. Airbnb may just be the next Ebay.

Notably absent from the list is Spotify, which offers unlimited music streaming on Android and iOS. It’s got 2.5 million paid subscribers and that number is bound to keep growing exponentially as more people take their cloud-based music library with them everywhere.

Did any companies on Goldman’s list surprise you? Which ones are missing? Here's the full list, according to TechCrunch:

Narrative Science
Ness computing
One Kings Lane
Peixe Urbano
Rent The Runway
Rue la la
Specific Media
Survey Monkey
Trunk Club
Warby Parker