Both - typically, staff uses their own mugs, and we have way more mugs in our kitchens than we have staff. At one point, when we were trying to be more "green" and cut our budget, the lady in charge of supplies refused to order styrofoam cups and told everyone to use the mugs. However, we are a government, and when we have guests here for meetings, you can't give them a mug with a brown stain ring in the bottom of the cup. We also have large scale gatherings with 20-50 people, where we'll put out the coffee pots and sleeves of cups for people to help themselves - it would be a lot of work and washing to put out that many mugs, and they are all different and don't match (not that looks should matter).

One last thing, we also started cutting down on bottled water, too. We bought pitchers for each of our 3 kitchens and matching glasses and use those for meetings as often as possible instead of bottled water. Staff also uses the glasses daily instead of the cups or bottles.