The waves of cash surfed relentlessly by some of Silicon Valley’s largest venture-backed businesses are showing signs of receding amid concern the companies may already worth more than they’re likely to be valued once they finally go public. Investors have created 132 privately held companies valued at $1 billion or more each, according to tracker firm CB Insights, including ride-hailing service Uber [UBER.UL], accommodation service Airbnb and messaging app Snapchat.