I have used the online form a couple of times to provide "feedback". They were very much along the line of " I love flying with Virgin, and these are the things that I noticed/experienced on my recent flight which could be improved. It didn't cause me too much inconvenience but I just thought I'd let you know".
I have always been really pleased with the responses from Crawley Towers -- a personalised response was always given, with a generous credit of miles to my FC account. I do get the feeling that my comments were taken on board seriously, and actions were taken as a result (which is really what I was looking for, not the miles, honestly). Wish I could say the same about those standard replies from BA... I do feel like their emails add salt to injury ("here're a few Avios, and unless we hear from you away we won't be looking into this"), but that's a topic for another day
I've never gone through to the top, not with VS anyway. Having used this method though with another business (a well-known department store), I was impressed by how quickly my email was responded to.
This is all a very long-winded way of saying that if something really bad has gone wrong which you might want to raise and resolve immediately, email the CEO. If it's something that you want to complain about, or flag to Virgin, and you don't mind waiting for a few days (up to 2 weeks is the official timeframe, but in my experience much quicker), then use the online form.