I've tried it twice--neither has been successful and I think it was because I did not get it down to coals.
First time was a brisket that had such a yucky bitter taste that I tossed it out.
I also tried, just recently, cooking ribs over oak coals. I left out the water pan, kept the fire stoked down as much as possible, and experiemented with slow "grilling". Not realy happy with that result either.
I think what you really need to do is set up another grill (weber kettle?) where you keep a wood fire going. As the coals develop there, you can transfer to the WSM. At least, that is my theory I am going to try next time
Dale