I work from home but visit my brother's place (in the next city) fairly often. I wonder if Google Now would think I work there. If so, I wonder if there's a way to tell it what's really going on.
Also the home/work thing shows up in Google's information about you on Latitude - so you can approve/edit/delete - see http://www.tech-recipes.com/rx/27740/android-setup-your-home...