GTD is for people, who don't need it. If you're a really busy person, you're not able to follow the rules of GTD. And if you don't have a problem to work with GTD after some time, you don't need GTD.
GTD is a cult. It has its devotees who use it and devotees that are not able to use it, but it's still hot if they join the club.
Inbox is a repository that enables you to do any stupidity that ever comes into your mind.
Half of all the tags is only a way to procrastination, it allows you to think that you don't have to do this today and that you can actually postpone it.
GTD is like an analogy photography of our time. It's fine and you like it, but the practical contribution is minimal.
If you can do something in two minutes, it actually doesn't mean that it's good to do it. It is not important to do anything as far you are doing something, it's important to do things that make sense and do matter in your life.
We have hundreds of GTD applications on the market and most of the users are still waiting for something better, for something that would finally be the right choice. But if there are so many developers who can't develop the right app for GTD, something is really wrong here.
Without priorities, there is no direction. GTD helps you clean your head of the important things you don't want to do, but if fills it with unimportant things that you are wiling to do instead. Just keep doing something. Anything.
It's old. In the year 2002 we worked on absolutely different bases, without messengers and social sites.
How many really successful people use GTD? Successful people concentrate on what they are doing, not really on the system.