When does the Mitzva of taking Challa apply? Does the dough have a need to have Challa taken from it, or does the baker need to take it? This leads on to a question about an electric breadmaker. With this you put in the ingredients, and 5 hours later a loaf of bread has been baked. How should one take Challa from this?

It is the batter that needs to have the Challah separated from, it's the Mitzvah of the dough's owner, yet anyone can do it for him; Same will apply for a bread-machine, the Challah has to be separated from the dough. However, only a batter larger than 1.2 kg of flour requires the separation of Challah, all bread machines I know are smaller in size. (Shulchan Aruch YD 324:1; 328: 3)