Very few cloud based solutions allow a person to concentrate on individuals and the tasks related to them. Futhermore, most desktop solutions are tied to one computer and fail when trying to use them on various computers.

One of the things I love about Remember the Milk is the Firefox addon to gmail.

For example I can see my day's tasks right beside my email.
However, the best thing is the ability to quickly add tasks. This fits right into my GTD lifestyle. Someone calls with a task, type it quickly. I think of something while triaging email, type it quickly. No having to switch screens with the inherent possibility of getting distracted. I go back later to the full RTM page and complete needed details for the quickly added tasks.

Furthermore its possible to concentrate on one contact at a time. This is enabled in the addon by typing "call Roger" the program will give you choices of Roger from your google contacts. Now when you get ready to concentrate on tasks for Roger you go over to the addon and choose to view tasks that are only related to Roger.

There is one needed work around. If you have not assigned an email address to "Roger" his name will not appear as a choice. I have devised a work around. I have a moniker that i use. roger@wit.com This allows me to still view tasks by contact even if they do not have an email address and when I see that moniker I know it is not a true email address.

Thanks RTM