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 —  Sarah Lacy via Pando Daily