Hey helgi,
this has been a particular problem of mine! I love GTD, even though it often is slight overkill for what I need (and sometimes is the only thing that actually works with the amount of new tasks I get)... but yeah, I often try out different "systems" and keep switching my organization schemes around so much that if I was able to just stick with one I would be able to get much more done. However, it always seems like that isn't easy!
Example: I'm currently LOVING a small Mac app called Inbox, but it's a very early and unstable beta. New builds are released roughly weekly, though, and I feel comfortable with this program as a final solution--it just isn't bug-free yet. So I'm waiting for it to get finished. My other options would be to go back to Hipster PDA (which I didn't like, due to all the rewriting of lists all the time), or switch to Thinking Rock (a cross-platform Java program), which is what I'm currently doing. Even though I have issues with TR, it's the "best" at the moment... but I can't seem to stop monitoring new developments in the organizational world as if they were somehow relevant to my life
My advice is the same as most people's--pick a system, get really comfortable with it (even its flaws!), and only explore new or expanded options if they actually would contribute to your PRODUCTIVITY (not the "wow" factor) in some measurable way. Example: understanding the limitations of paper yet tolerating them, then switching to a program which DOESN'T require a huge relearning but does assist with the exact flaws you previously identified with paper.
Really hard not to keep looking, though
