Being a GC player myself, I have to say that this tactic is a huge bunch of boring cow manure.
Sure, it works. But it really is no fun to either side. I would use it in tournaments or such, but I have always been a gamer that would make lists and fight in the spirit of the army. Grey Company spirit is "For Arnor!" I will move up slowly, whitttling down oposition before finally charging. Or back up with one unit to lure, and jump the flank with another. GC has a lot of possibilites besides the shoot, run, shoot, run, and it is people like this that really give it a bad name.
As for mostly new guys playing, I have to say. I am the only new guy in the shop who plays them, out of...well a lot. Isengard and Minas Tirith are the most popular starting armies.
Yea, fight me, and it would be an exciting game. I prefer charging trolls just to see if I can hack them down.
PS: Worked on a Mumak!