Do most planes have steerable landing gear?
Actually, no. Most planes are, in fact, taildraggers!
Is it a good thing to have or not.
If your model has nose-gear, it absolutely NO QUESTION ABOUT IT has to be steerable. That having been said, I absolutely hate nose-gear models and will never ever again fly one (unless someone happens to give me a P-38). Seriously, I converted my very first trainer to a taildragger after about the third flight. And every model I've had since is a taildragger. And in most cases that tail wheel hasn't been steerable at all.