At my favorite places that are doing take-out I tip about 20-25%. I really want them to remain and helping out their employees seems reasonable.
There is a place that started adding a 20% surcharge which does not go directly to the employee - it's for medical care and a boost in wages for the kitchen help who don't share in the tips to give them a wage that is closer to what the tipped employees get. I don't like that system; it leaves me confused about how much the employees are actually getting and I don't want to have to be an expert on our two stage minimum wage law or how much the medical is really costing or helping them. I also don't appreciate that it's a tiny note on the bottom of the page of menus. As Zloth said, if it's a mandatory charge just raise the prices of the menu items to indicate what the real price is. I don't need to have your cash wages, medical care costs, rent, utilities, and ingredients all broken down for me on the menu. I just don't go there anymore. Anyway, their food was good and their service was good, but their real specialty was wine - one of the great cellars in the region, or so they say. And I just don't care that much about wine.