I think the playlist feature is awesome, but it's not implemented very well. when you right click on a game and try to add it to a playlist, it doesn't show you the playlists it's already in. also, if you add it to a playlist it takes out out of the playlist menu to tell you you've added it to that playlist. This is really not very user friendly. when you have thousands of games, it's hard to remember which games you've placed in what playlist. it would be much easier if the playlist menu just contained a menu with all your playlists and tick boxes next to them. then you can simply look at a game to see what playlists it's already in. This would be vastly more user friendly and extremely useful in big box mode too. Also you wouldn't have to go to the list to check what games you have on there or to delete a game from a list. you could simply do it from the game. I'm sure there are many more practical reasons too.
I think that by thinking about the code, you'd have to add arrays to the games so they contain the playlists but the method that it has atm is really annoying and time consuming as well as prone to mistakes from the user.