It would be great if the Quick Add bookmarklet would capture the URL for the page you're on when adding a task.

Often the page I'm on is where I need to be when I am going to complete the task (e.g., buy tickets, or refer back to Gmail message, purchase something oline).

It's not always the case, but the URL could always be disregarded if it is not relevant.

Or maybe you could put a little "x" next to the URL in the bookmarklet pop-up so it can be removed if it's not relevant.