I think the air conditioner in the dining area (being an inverter type, Fujitsu ASTG30LFCC), when on, generates RFI that degrades my internet connectivity (or the Wi-Fi between the NBN box and my PC, anyway); while I've had it on to heat, my connection has dropped out left, right and center.
(I bet the amount of filtering incorporated into those units is the bare minimum needed to pass the mandatory standards. I'm sure the use of an unshielded 3C+E cable to the outdoor unit doesn't help, either.)
Consequently, I've ended up resorting to the Kambrook KFH660 (my house is quite small, so 2.4kW is enough to warm it noticeably, though not drastically).
So much for saving electricity, but at least my internet connection seems to be holding up better. We do also have smaller units (Fujitsu ASTG09KMCA) in the bedrooms, but those don't seem to be ruining my connectivity (or at least, the one in Mum's room doesn't; to be fair, that's at the opposite end of the house).
How I'll cope with summer is another question…