But we settle in for another winter. The best companies — Airbnb, Dropbox, Evernote, Spotify, and of course Twitter — are trapped with $1 billion-plus valuations. In some cases, the valuations are for multiple billions. What yielded a bragging press release at the time is now looking like a gilded trap: They have to go public, do a down round, or sell for a smaller price and largely be viewed as a failure. And that means — as Libin hinted last week — it may be in for another eight years before we see some mega-cap consumer Web exits.