Actually they've had this policy in place for a while. DHS is just letting us know about now because of that one case in LAX 3 years ago made headlines. The US Court of Appeals basically says it's ok for DHS to search all your belongings when entering the country. Now they have just branched it off to an offsite location. I'd rather let them have it and have them return it later than wait around for hours for them to clear it. Of course, I'm sure if data is destroyed, it's not their fault. 
Here is the lowdown of what they can and "cannot" do:
search_authority.pdf
Here is a list of things to do for those who travel often:
1. You should not carry any confidential, personal information that you do not want examined by third parties on your computer – or other electronic devices. This includes financial data, photographs, and email stored on computers, wireless phones, Blackberries, or iPod-type devices.
2. Limit the amount of proprietary business/personal information you carry on your computer, and that it be transmitted before crossing the border so you have access to it in the event your unit is seized.
3. If your laptop also serves as your main computer, get another one for travel purposes.
4. Don't try to hide data(encryption etc) from U.S. border authorities, but to take steps to minimize the impact of its loss, or the inability to access it, in the event it is seized.
I wouldn't worry too much. Only if you're an older guy coming back from Sri Lanka, Thailand, Philippines or Indonesia would they suspect you of having childporn. If you're of Middle East descent, you know they are not profiling just because they pick you for all the checks 
I now just upload my important work files to a secure server for download when I get to my place. No sensitive data on my laptop anymore. I am also sending my backup drive via fedex with one copy of my pictures/videos incase the laptop gets stolen,damaged or something. Brave New World.