I was playing on a huge map the other day and thought it might be a neat feature to be able to mark an explored planet for colonization with a scout ship. This need not have any game impact but would be helpful to remember where a good star system is.

Having the ability to set flags of some sort would be nice, but could be a bit complicated. If they had a built in reminder system that would be very useful. Too many times have I thought about colonizing somewhere and then 50 turns later remember it and see it is already part of a neighbour's empire... A little "You still haven't colonized this tagged planet" reminder would be nice every 5-10 turns