(in a nutshell...) I like the Getting Things Done (GTD) method for organizing my life and am using it more and more often. I work in a few different places using all three major operating systems: Linux, Apple and Windows. Gmail is containing half of my important information. So, I needed an a Time Management tool that I could use it anywhere, would be flexible, highly customizable and also include Gmail as one of the main options. I also use Treo syncing it with Google Calendar via GCALDaemon, thus Google Calendar had to be implemented as well.
I tried Thinking Rock (with Dropbox), GTD Inbox, Vitalist, and Todoist.
I ended up using Gmail with Multiple inboxes, displaying Google Calendar as gadget, iGoogle with multiple tabs for the various locations displaying one or more Google Tasks. (read more)