Khagani heard that if you leave a planet and come back all the stuff will be different. so all of your stuff that you worked on all those hours gone in seconds. that kind of sucks. idk if thats completely true though
I'm not sure if this is correct or not, but in a video I watched the lead designer said something alone the lines of "when you leave the planet, it's all gone. The grass, trees, etc etc." It sounds like he means your progress is also gone, but I took it as he meant it is no longer rendered by the game. At the time he was talking about how the interstellar environment loads all around you as you move throughout it, so I assumed by him saying "it's all gone" he just meant it is no longer using up resources. As I said though - he could have meant everything changes and your progress is lost. Which would be a deal breaker, IMO.
Overall I get a very similar feeling from this game that I did from Spore. Thankfully EA doesn't have control over this one, so hopefully it will be better than the massive letdown that Spore was.