We used a 3lb rib eye round roast (about $8/lb at Whole Foods, cheaper EVERYWHERE else) and it fed 6 people with a good 3 servings left over. I would say expect 1/3lb/per person.
Rub the roast with olive oil (use your hands), sprinkle on a ***liberal*** helping of salt, pepper and roasemary on the exterior. I also like to use garlic powder. Make sure to coat both sides. Let the roast enjoy it's rub for a few hours in the fridge. Or not. It still tastes good if you don't have the time to let it hang out.
Preheat the oven to 450-500 degrees. Throw the roast in for 20 minutes then turn the heat down to 350 and cook for about 1-1.5 hours.
It should be pink in the middle =)
On that note, since we received a meat thermometer as a kitchen gadget for a housewarming party, we used it to stop the meat when it had reached 140 degrees (this was too medium, I would think 125 would be better)
NOTE: Allow the meat to rest for a while before cutting. 30 minutes at least.
Cut into thin slices. Enjoy!