One of the best features in Remember the Milk is the smart list, which is essentially a search option, but your searches can be saved permanently. Normally you would want to save a search because you perform them often, but in Remember the Milk there are more benefits.
I actually only have one “real” list in RTM, the others are all smart lists. So I have loads of tasks, all in one list, but tagged well. This means that if I search for “tag: blog”, it will show me all my blog related tasks. If I save that search, I now have a new list, with every item tagged with blog. The productivity aspect enters right here, because you aren’t limited to just viewing, you can edit and create tasks inside the smart list.
This means that if you create a task, it will automatically be tagged with “blog”, and of course it will be created in your primary list. This feature is great if you do some more complex searches, like incomplete priority 1 tasks, tagged with “blog” and due tomorrow. These are you most important tasks probably, so you may want to keep an eye on them. You can either type “priority:1 and status:incomplete and tag:blog and dueWithin:”1 of today”" in the search field, or you can use the search options too. When you save this as a smart list and create a new task, it will automatically be assigned all these attributes. This saves you time, increasing your productivity because there is no need to tag all your tasks.
I recommend having only 1, maybe two main lists, and creating all your other lists from them using smart lists. This makes sense from a GTD and productivity view, possibly even database management view because it eliminates redundancy, and auto-creates what you need. I also find that sometimes it’s useful to see all your tasks, regardless of their properties in one place.