I've integrated Reminders into my GTD system in a way similar to what is described here for Evernote: http://examinehealth.com/personal-productivity/69-gtd-and-evernote.html
Originally Posted by silvine
I have separate lists for my inbox, single actions, and individual projects, with project lists beginning with a period to help identify them more easily. Because Reminders doesn't have tags like Evernote, I add context tags manually to the end of the entered item (e.g., "Call Jason re: conference @phone"). This allows me to use the search function w/in the app to find tasks appropriate for any given context.
It's certainly not a perfect set up, but I find the convenience of Siri along with the native apps in OS X and iCloud.com to outweigh any shortcomings.