I started wearing PJs when I was given some on SQ, LH and LX flights in first earlier this year. They are so much more comfortable. I brought along my own LX and LH pajamas when flying ATL-PVG-ATL earlier this year and slept like a baby in the 77L flat beds. (Some sleeping pills certainly helped.)

I will definitely do so in the future for all intercontinental premium-cabin flights in which sleep is involved. Unlikely to do so for US transcon redeyes or economy flights though.