The yield of meat will be the same as if you were cooking the same cut of beef in a smoker. Thus, if you cook a chuck, no bone, and expect a 60% yield (40% loss, dry wieght), reasonable, then you would expect the same of meat done in a crock pot. The difference being, of course, you end up with gravy and veggies. Assuming you would feed 1/3 pound, dry weight of meat, then you need to start with somewhere around 2/3 pound of meat for ease of math. I still think 1/2 pound of meat is a decent number for a mixed crowd, thus 1/2 pound +/- per person.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."