I installed an Aquia about 5 months ago and have some additional comments...
1) With regard to smearing. Even with the Toto seat it smears a bit more than the toilet it replaced (Kohler Welworth). I wouldn't call it smear free, but it is much less of a problem than I expected considering the size of the wet area.
2) It has great flushing performance! In the 5 months the hideaway Oxo plunger sitting next to the toilet hasn't been used once. With the Kohler that plunger got used several times a week.
3) You do hear more with this toilet than any other I've ever used. That's not to say the flush is overly loud. As liquids enter the bowl, you hear the water being displaced down the drain. If it's very windy outside, you do hear a bit of water being sucked down the drain from what I assume is a slight temporary vacuum being created in the vent line.
4) When you do the .9 gal flush, you have to learn to push down on the button and hold it down for a small fraction of a second. If you push and release too quickly, the bowl doesn't clear 100%. My technique is to release as soon as I see the first hint of water washing down the sides of the bowl.
5) Being the first toilet I ever installed, I can't rate it's difficulty vs. standard units. That being said, it wasn't the easiest home project I've ever undertaken. Our Aquia is installed on a tumbled marble floor. I thought the drill sizes listed in the directions were VERY tight for the anchors provided. I would have destroyed the anchors if I tried to put them in the specified holes. I also had concerns because the plumbing rough-in was about 1/2" shy of the 12" that the Aquia specifies. Luckily it still went in fine. The Aquia directions also call for a water supply rough-in that's several inches wider than typical. Our existing water supply used with the Kohler worked just fine and that was several inches narrower than Aquia spec. Because of the tumbled marble, I did have to use several plastic wedges around one side of the base because of the flooring. That has also been fine. The last installation issue was finding a seal that would work going into the toilet drain. A plumber we had at the house several years ago cautioned against using any kind of wax seal when you have a marble floor. I tried using the Fernco wax free seal, but it wouldn't seat properly as it wouldn't fully recess into the flange. Ended up using the Fluidmaster Wax Free bowl gasket which seemed kind of lightweight and a bit cheezy compared with the Fernco. I had no issues with the tank bolts or any other leaks (and didn't need to sand either).
6) Did I already say the flush performace is outstanding!
The Aquia has a small learning curve, but I would buy it again in a heartbeat.