Yes, we use Atombox for doing GTD, along with Google Calendar. I also keep a lot of small reference and support atoms in there, too (like the size of the tires on my car and wines I like).

We do have some ideas about notifications that we might implement in the future but it's not necessary to have notifications to do GTD. Access to your lists wherever you are is the linchpin for that use case.

Thanks for your comment.