Yes, it mines google latitude data for that. Since I left my office job and started running my own business from home. Latitude has been getting very confused about where I work. Last time I checked it thought I worked at the local shopping centre.
Edit: Just checked, it now thinks I work at my kid's school.
Your preferred credit card issuer already knows this - if you have a propensity to eat out during the week. It can look at where you are eating most of the days during the week, aggregated over time, to guess which part of town do you work, vs your home (it knows your home address). It can also look at your spend at gas stations over time to see if you own an SUV vs a Car, or whether its a fuel efficient vehicle or not.
Aggregated data from a number of different sources can give a near-complete picture on a customer.
Edit: Just checked, it now thinks I work at my kid's school.