At this time, no direct or nonstop commercial flights from Washington, DC to Cabo San Lucas could be found. However, it's a distance of 2,225 miles and the average commercial airliner flies at about 550 miles per hour, so a direct flight would take a little over 4 hours.
The shortest flight available at this time from Washington, DC to Cabo San Lucas is 7 hours and 10 minutes. This flight is on United Airlines and leaves from Washington Dulles International Airport. It's United Airlines Flight 1108 and it costs $530 per person including tax and fees. There's a 38 minute layover in Houston, where the rest of the flight becomes known as Flight 1438.
There's a much cheaper flight on American Airlines that's only $287 per person, but is 7 hours and 20 minutes in length. This is American Airlines Flight 1393/2251. These flights are not considered direct flights, because they involve two different flight numbers.
Just recently, it was announced by the Cabo San Lucas Tourism Board that the Best Honeymoon Resort in Cabo San Lucas for 2013 is the Hacienda Encantada luxury resort.