That would depend on the game in my opinion, I would go about it by saving particular variables that are specific to that level/game to a text file or similar then loading it up later when required. This way you don't have to rely on the "System" functions which tend to not work on regular occasions (as well as other functions). Although, the only problem with using a text based file is that without encryption it could be easily changed.
I wouldn't say that they don't work, it's more that the documentation is awful & it's hard to know how to use them.
