There needs to be a real set of goals and missions, weekly, monthly, yearly that proceed any GTD setup. Otherwise its just a big list with no "juice" to it. Every time you tick off a task, it needs to be taking you one step close to your larger goals.
Put another way, if you are a sculptor and you just "chip away" at all different random sculptures its hard to see the progress. Instead if you are working on one or two large scultpures, each chip is closer to your bigger goals. You can look behind and see progress, look ahead and see momentum.
This may help...here is a shameless plug for my podcast:
RSS - http://www.fmstudio.com/podcasts/rss2
iTunes - http://phobos.apple.com/WebObjects/M...st?id=73331288
I talk a lot about the methods and concepts that happen before you even set up your GTD
Bear in mind this happens a lot, and yes you can set up omnifocus different ways, but that does not always help.