Radiant heating. It's become more popular lately, but it's not new, having been around since the Roman Empire. I hadn't included it in the original plans since we already have a nice forced-air furnace, but the more I read about it, the more it makes sense to install some while I've got the floor ripped up. The kitchen currently relies on heat from the occupants and appliances, and whatever comes from the adjacent rooms to stay warm, but we're planning on tile for the floor. It'll still be as warm as now, but will feel cooler because of the tile.
Similarly, the new bathroom will have a tile floor. Katarina gets up early for work, and while a bath mat helps, it'd be a lot more comfortable if a timer-based radiant heat system warmed things up for her on those cold winter mornings. It usually doesn't get that cold here in the SF Bay Area, but we do have the occasional freeze, and we even get snow at our elevation every 5 years or so. Still nothing like my parents' house back in Michigan (though who knows what global warming is going to do to various climates affected by changing ocean currents), but comfortable is comfortable.
The addition is so much better sealed and insulated than the rest of the house that it's been pretty comfortable even though the heating duct isn't connected to the furnace yet. So I don't expect either zone to get that much use compared with the forced air for the whole house, but it's a lot easier to install now than later. I do wonder how California's Title 24 compares with Canada's R2000 standard for the energy part (R2000 also specifies green building techniques, like low VOC paints) and how that compares with what I've built. I know I've exceeded Title 24 needs by anywhere between a little and a lot, but the whole house is only as good as its weakest point in a lot of ways. The fact I've been insulating stuff during the remodel, installing dual-pane windows, etc. helps, but it'll never be as good as the addition.
I've been busy reading up on it on That Home Site! (thanks for the pointer, Azar) and on the Healthy Heating site. That's been one of the fun things about this project -- learning new skills, new techniques and new technologies. Whee!