Download the Mobile Passport app from the App Store. We just got to LAX Bradley Terminal, and the Customs and Border Protection line looked to be ~3 hours.
The currently unpaid US government workers there were trying hard to be helpful, and one thing that allowed people to save 2 hours was downloading the aforementioned app.
Unfortunately, WiFi or phone signal to download the app is not good once you are in line. So do it in advance, and you can save yourself some time (and reduce so of the wait of others if you had to use their scanners).
And be nice to the CBP people — they are working but not being paid at the moment.