I've tried and failed a couple of times to adhere to a GTD system. There are some habits from GTD that I've found are useful outside of the whole system. I've written a blog post about this here http://www.lifebutbetter.com/gtd-lit...g-things-done/.
I know this may be a little controversial because it's a long way from rigorous GTD but I hope that you can see some benefits in it.
Let me know what you think.