Still nice to feel sore for the next couple days, sometimes its a nice reasurance that your workout was intense enough... 
Sure, it's a nice little bonus, but in terms of muscle growth i don't think it's all that important. For example, I could do the same chest routine 2wks in a row, everything exactly the same, weight, reps, time frame...everything. Wk 1 not really sore, wk 2 sore as crap. Then I might do something completely different the next wk, no real soreness, the next wk something different again, and really sore. Each time I pushed as hard as I could...does that mean on the days where I didn't get sore my workouts were sub-par? Not hardly. Muscle growth is equated with stimulation, if soreness occurs, great, if not, great...as long as the muscle worked was adequately stimulated it should not matter.
I'll be honest, for years this was something I could not grasp. We all have a tendency to brainwash ourselves into thinking one particular thing is best. Take for instance training volume...more then half of us here at one time truly believed that the only way we were really doing anything in the gym was if we pounded as many sets per workout as Arnold said he used to do. Basically we brainwash ourselves into one way of thinking, and it's very difficult to re-brainwash ourselves in the right direction.