A common programming quote I see every day is:
Premature optimization is the root of all evil!
I admit I'm one of those guys that like to do premature optimization in a pretty obssessive manner but that's probably because I'm not aware how powerful modern processors are. I can think of lots of sollutions for a problem, but all of them are tough on the memory side, and I keep thinking "This will hurt me more in the future when I'll have to re-do it because it's bad performance-wise."
How do you know when the code you are thinking of is going too far and is not a case of premature optimization? How much can your game handle at a time before performance becomes a problem?