The forums and blog have tons of great information about how to program smart lists to do some amazing things.
For example, it is very helpful to me to create tags for 'sleeper tasks' that should not show up in a smart list unless they are nearly due. I can create tasks with #z3d that will not show up unless they are due in 3 days or less. This is accomplished by creating a smart list eg 'zzz' that lists all sleeper tasks not nearly due, and then adding 'and not list:zzz' to any smart list that you want to hide distant tasks from.
There are many other tips in the forums, and an advanced user manual where these things were described in one place would be wonderful.
This is also helpful:
Posted at 6:26pm on May 23, 2011