Notes:
If you see a packet will hit your planet next turn and you don't have a freighter already in orbit, there is nothing you can do; the packet will hit before you can build a mass driver or defenses and before you can get any freighter there to move the pop.
If you plan on abandoning a planet to an ally by moving a freighter to the planet with orders to Set Waypoint to 1(00) on the same turn that the ally moves a freighter to the planet with orders to Unload All, the ally will face your entire population, not just the 100 colonists you had intended (a very painful lesson).
Remote Terraformers are very effective against narrow-hab CAs since they terraform *after* the CA instaforms.
Since SD mine detonation occurs between fleet movement and production, the arriving enemy fleet can be damaged while the fleet that you produce that turn can enter combat undamaged.
If you intercept an enemy freighter going to meet the MT, you can prevent him from trading.
A fleet that you give away will still be yours until the end of combat (pre-"i" patch allowed waypoint 0 fleet transfers).
A fleet with a waypoint 0 load task in orbit around a planet that you don't own will not proceed to waypoint 1 (very painful Robber Baron lesson).