Almost 70 million people enter the USA every year - that's over 190,000 per day. We hear about 2 or 3 horrible stories and it seems like every tourist who enters the country is harassed by immigration. I totally understand the concern when one hears these stories though, it's important to keep in mind how incredibly rarely they have occurred.
I would say your chances of immigration even looking twice at your laptop are extremely small. When they want to look at any electronic device, generally the only thing they want to see is for you to turn on the power to prove that it is an actual working device and not just an empty case with explosive materials inside it. They have no interest in whatever data you have on the device.
Exceptions might be if you are involved in high profile, anti-US politics or you suspect there is some reason you would be a person of interest to the US homeland security. Or if you are entering illegally, planning to overstay your visa or doing anything which you feel you will have to lie to immigration as you enter the country. In those cases I would be concerned entering any country, not just the US.