I think you shouldn't go to other people's videos or twitter accounts and post messages like "follow me" or "subscribe" but at the same time I know how hard it can be for people to find an account that doesn't have many views or followers or subscribers. I have a YouTube channel that I do machinima on and the number of subs I have is pretty small because I haven't put anything significant out yet. My worry is that when I do put out my machinima that I am spending so much time on, no one will see it. Businesses and products and companies advertise all the time because that is how people find the products they are looking for. I don't think it should be looked down upon if someone wants to do the same on YouTube as long they have something to offer and they aren't just looking for subscribers and followers just for the sake of having them.