Hi all,
On a nearly empty DEN-LAX UA flight on January 1, 2003, I took a snooze in an empty row of five. While across all five seats, I always had my seatbelt across my waist.
I was amazed when they didn't even tell me to sit up for the landing...so I didn't.
Of course, the key to getting a row of five to yourself is to ask at the gate for the rows where no one is assigned. Then, sit in the middle or next to it (never on the aisle), and spread a jacket, bag, and blankets/pillows across the other seats. With a mostly empty plane, your row will be secured!
Later,
Tim in Hollywood