I was actually thinking about how nice their webapp was to use while I was doing them, too. _Incredible_ amount of complexity to reduce to a really usable app.
I think an interesting thing about turbotax and ifttt is that they both were confronted with the problem of a really hard UX and they both decided that the simplest solution was just to make everything a series of modals with the absolute minimum number of decision points. Kind of like the game Reigns.