Eddie Smith from practicallyefficient.com:
I think one reason that OmniFocus overwhelms some people is that it forces them to confront just how much they have going on.
I've been using OmniFocus for a couple of years now and today find it essential. I have all the versions (Mac, iPhone, iPad) and keep them in sync via MobileMe. All this magic helps me remember what I need to at the right time.
But there was a time when I was completely confused and overwhelmed by OmniFocus. Coming from writing my to-dos and reminders on pieces of paper that I always lost, to then using the to-do functionality in Mail.app, I found OmniFocus a tough app to get my head around.
I knew I needed something more sophisticated than a simple list where I could check off items as I finished them. I had so many things going on that I was always overwhelmed, never truly feeling like I was on top of things.
Once I got the hang of OmniFocus and the GTD system, the first thing that hit me was the amount of things I had going on. I had committed to so many things that I wasn't truly focusing on any. The best thing I got from going through this process was that I just removed a bunch of stuff from my life that wasn't important and I put a few projects on hold that I knew I couldn't get to at the time. This allowed me to focus on what was truly important.