Yeah, and that tends to be the main problem with things like this. Since you're cutting the game off as it's saving, you're stopping it before it saves all of your data. So even if you don't lose anything that's apparently "vital," like your Pokemon, items, etc., you are going to lose some of those hidden lines of code. Over time, this can destabilize your game (even if you only use such a cheat once) and accelerate any problems with your cartridge, as we've discussed in the forums for the older games.

But if you don't mind such issues, and if you don't have any qualms with these methods of duplication, then this is an excellent technique. Besides, Diamond and Pearl will be released soon anyway. Unless you just exploit that Emerald game to death, it's not as if the cartridge will die before you can get DP (thereby always having the newest generation of games). So if you're okay with techniques like this, then go for it!