Nice on. Much like popsider says, you can use the FTP to give yourself training zones. So for a 40kmTT you'd typically train in the Threshold zone. Top end of same zone for 10mi TTs or sprint tris. IM would be endurance zone.
Coggan and Allen's book Training and Racing with a power meter is a good background/base for knowledge.
I hate the 20 minute test with a passion. The one I do has a 5min all-out after the 1min reps and before the 20 minutes. I gather it is to ensure there is no anaerobic component to the 20 minute AP.
Edited: 08/02/2013 at 23:04