Paul,
Honestly, I haven't tried to grill anything from start to finish on the WSM. The only time that comes close is when I cooked Andy's Jerk Chicken on my WSM. That's a recipe in "Weber's Charcoal Grilling." It calls for barbecuing bone-chicken parts for a couple hours. They taste great at that point (awesome marinade), but the skin is a little rubbery, so you need to add some charcoal and grill the chicken over a higher heat to crisp the skin. It works really well, so I can imagine grilling other foods on the WSM. Having said that, one of the reasons I prefer the kettle is that it allows me enough room on the charcoal grate to for two or three different heat zones. That kind of flexibility is key to top-notch grilling, I think.
Jamie