With condolences to lien :-)
Starting March 30, 2014 United's two daily services SFO-SYD and LAX-SYD (together with the continuing SYD-MEL) will switch from Boeing 747s to 777s. The first of these to fly SYD-SFO/LAX will operate on April 1.
The plane will be an sUA three class 777, with 8 seats in Global First, 40 fully lie flat BusinessFirst (that's Business class), 104 Economy Plus and 117 regular Economy.
The most noticeable advantage is that the economy cabin has in seat TV screens with full AVOD, allowing you to select from dozens of movies and TV shows. The economy seats are also modern and thinner, but still comfortable imo, giving more legroom for the same seat pitch. They also have the intelligent recline whereby the seat cushion moves forward a couple of inches so that the recline intrudes less on the passenger behind.
Well smaller capacity (16 fewer premium cabin seats and 89 fewer in Y) meaning fewer upgrades and possibly fewer ultra cheap economy tickets. And for those who may have started using the WiFi on the 747, the 777s don't have that.
I've flown both the 747 and 777. Although I prefer the 747 in Business because of the upper deck, I much prefer the 777 in economy.Edited: 10:22 pm, August 17, 2013