A lot of people are put off by this mega event, so I wanted to post my recent experience with it. I will start by saying that I was in a decent position when the Jagged Knife happened, not evena t war with anyone else at the time, and I still had the gut reaction of "Well, this game is about over." But I don't like to give up without a fight, and I decided to make the best of what was left.
The JK took six of my fourteen planets, all around the rim of my civilization - they don't seem to grab your core planets anymore like they did in the beta. All of the captured planets had 16-18 billion population and were in the last stages of upgrading to industrial centers and VR centers, so in that one turn I lost a lot of production capacity, and the newly hostile planets had huge populations and would be hard to get back. I lot my tech capital, and four of the other taken planets were PQ 16 and above.
However, they did not get my two starship-building powerhouses, my Tir-Quan Training, my Hyperion Shrinker, or my gravity accelerators. I revived an old DL practice and started bulding Vengeance-class transports - a tiny hull with one advanced troop module and a single warp IV engine. Every starport-equipped planet could build one every 1-3 turns, and they didn't have to go far, so they didn't need to be fast. I also had two neighbors at war with each other, so I was able to buy a big transport off one of them to supplement my invasion forces.
I sold a lot of my older starships to one of my neighbors for ready invasion cash, leaving my top-of-the-line spacefleet to deal with JK defenders. Once the transports started to build up, I started taking back my planets, one bloody invasion at a time.
Finally, I had all of my planets back, though my economy was sagging from lack of taxpayers. I stopped building starships at all and ratcheted down my production until my population could build back up.
The best part of the whole event was the fact that I build too many transports. Oops! Well, some of my neighbors had also lost planets on the fringe of my empire to the JK, so I started taking them. Including a pink star PQ26 planet that turned out to be a fully-built-up manufacturing capital.
Now, only a few months after the initial JK event, I have all of my planets back and I gained seven more, and I'm not at war with anyone. To top it off, the JK forked over a treaty and a bunch of cash when I offered peace (after I had used up all of my transports

). I finally got there about 1:00 am last night; now I just have to figure out wherether it's worth it to lower taxes and quit building anything to get the 100% population bonus, or should I try to have it both ways?