2. Scrum is not suited to planning system test cycles
The reason for the (Ha Ha) in my first post in the series is that our iterations are not actually potentially releasable. We have a suite of tests which are not run on a continuous basis which need to be executed before release. These include platform testing, performance and stress tests - we also have (to our great shame) some manual UI tests.
The point is that we need to go through a system test and fixing cycle before we ship any software release out the door. When we need to do this SCRUM does not help. Scrum relies on your ability to predict upfront what tasks you are going to work on and to estimate them - clearly you do not know what bugs you are going to find so you cannot use scrum to manage this
While Scrum is good for software development cycles - use a standard test plan and for system testing.