Today I registered my trip with the Department of State. I usually register my trips with the DOS when traveling internationally. It's probably not necessary, but just in case of some huge event I want the US Embassy in whatever country I'm visiting to know I'm there so they can keep an eye out for me.
Here's what you do:
You can find all sorts of useful travel information about various countries. This is also where you can look to find any travel advisories that the US has issued. Travel advisories can affect your travel insurance. Some policies are void while traveling in countries that advisories have been issued against, so make sure you are covered and traveling safely.
At state.gov you can create a profile and follow their online wizard to create itineraries. Once you've filed itineraries with the DOS, you will be added to local embassy lists of travelers.
That's it. Easy.