I agree with you about having an application that you have with you all of the time. That does make all the difference.
I used and taught Covey and Daytimer for many years before reading David Allen’s GTD book and switching to GTD. And then I found an application that allows me to view my entire GTD at work on my Win machine, at home on my Macs and even on my cell phone. And another app lets me call in tasks to my GTD without any writing or typing, great for those thoughts that hit me while driving. I’ve written about my experiences with GTD in a blog post at http://johnkendrick.wordpress.com/2008/03/27/more-getting-things-done/ John