I'm constantly trying out new tools and technologies as I'm a total gadget and technology geek. But I've been using my list manager for 3 or 4 years now (eProductivity on Lotus Notes) and nothing has come close to substituting it. It just works in my system.
I am happy to challenge to system on a regular basis because it helps me feel attracted and comfortable that I've really got the system that works for me. And besides, if I didn't keep challenging it, I probably wouldn't have noticed and tried eProductivity which has actually helped me implement GTD. The "Weekly Review Coach" is still what I use to this day to do my weekly reviews even though I could probably remember the steps without it. I even use the Get Clear portion of the Weekly Review Coach for my daily mini-reviews when I feel like I need that guide.