Hi Alex,
I have a house in Slovenia and I find that collecting tourist tax is now the biggest time-eater of everything that I have to do in managing the house - getting guests e-mail, getting details, chasing them, making a note of whether i have chased them and whether i have their tourist tax!. AirBnB 'help topic' on Tourist Tax, say that hosts should mention it in their listing yet there seems to be no-where to actually do this. Other sites (HomeAway, TripAdvisor) allow me to put notes in to that effect so at least guests know that it coming. With AirBnB you have to magically remember to mention it BEFORE you accept (which I don't always remember to do) and then guests get annoyed (quite rightly) - as if AirBnB want to trip you up and annoy guests!
I really hope AirBnB to allow these notes to be added, or even allow hosts to include it in the calculation; but every countries/regions tourist tax is different so they have to just allow ANY combination of price/age/nights etc - not that hard really.