The 780 has an additional benefit of being able to provide optical out without an AC adaptor. So if you ever need that... I use the batteries when I record to MD just to reduce the clutter.
Also, does this bug anyone - Panasonic's electronic (no, not digital) volume control is in 25 steps. Regardless of amp output, 3/25 is too quiet and 4/25 is too loud for efficient earbuds (like the E888) in a quiet room
past Panasonic schedules suggest an early-2002 arrival. Probably first quarter? The launch date for Japan was October 1.
A lot of people think you can use 100V Japanese-spec AC adaptors with 110V North American wall outlets without trouble. However, you might want to pursue absolute peace of mind, and get a 110-->100V transformer.
Panasonic CD players all use the same 4.5V adaptor. Well, they're all 4.5V, but some provide less power than others. Some are rated at 800mA, some half of that. An alternate solution could be buying a 4.5V adaptor from Panasonic, spare part for the 780 for instance.
If you have another equipment that recharges "gumpack" batteries, you can also do that and save yourself the trouble altogether.