I am also a road rider who has recently started mountain biking. I bought the Stumpjumper FSR Expert with the "Brain". I am really sold on the brain. It really works like a hardtail on the smooth areas and is great also when I get to the rocky technical areas. Most trails that I ride contain both rough and smooth areas and with the brain I don't have to compramise with a setting that is not quite right for the rough or the smooth.
All that said, the brain on my bike is currently not functioning properly. The bike is ste up fairly well so I don't notice a lot of bobbing on smooth areas but I do feel some. I'm still waiting to see if this issue can be resoved.