Save states usually work great (90% maybe?).
However, they're not totally reliable. Use in-game saves! if you have problems, use the in-game save to restore. I use save states as a quick backup, or as a "redo" beofre a hard part / difficult choice in the game. But I always use the in-game save. There is NOTHING sorese than needding to replay parts of the game you've already done ... the longer you have to go back, the worse it is. I talked to a guy a while ago about an issue with FF (I think it was 7). He had to go back 4 or 5 hours. That's rough .. but at least it wasn't 8 or 9 ... or 10 or 20!
Also, as schtruck said, you can load up a in-game save via memory card, then try restoring a save state.