If you start a new game (or load one of the working saves) and save, can you load that save during the same session (if you don't quit or switch profiles)? Or does the game freeze or hang if you try?
There are two problems in OSX which have similar symptoms. The first is just an issue with the saves being displayed in the load window, but the save themselves are ok; this can generally be fixed by the suggestions above. A much rarer problem (also reported once in Windows) involves the saves being corrupt during the save process, so even while they are shown in the load window, they will not load properly. In that case the only workaround that I know of is to play from a different OSX user account (one person had this happen in their main account, with their Documents folder moved to a Dropbox folder with a symbolic link, but if they played under a new account with a default Documents folder it would save properly).
