I've never cooked sous vide before, but am now equipped to try thanks to the holidays.  We have a 3 pound chuck roast -- I'm not sure what the exact cut shape is, but it's vaguely cube shaped. If we cut the roast into steaks (1-2 inches thick) before bagging and cooking, what effect would this have on the cooking time and/or quality? 
Sous vide cooking is a function of temperature and the surface area to volume ratio of the food in question.  If you have a high surface area to volume the cooking time will be shorter. Steaks would have a higher ratio than the roast so they would take less time than the roast.  The amount of the time difference is difficult to predict exactly over such a long time scale, but a rough calculation of the ratio I spoke of would be a good starting point for a compensation factor.  If you have the time and your water bath can accommodate, I'd suggest keeping the roast whole and finishing in a skillet.  It's much more impressive than a steak. 