I hate it when one of your 'friends' challenge you to a friendly without your knowledge. They do not know what kind of state your team is in.... whether you've trained your players a short while ago, whether you have injuries, whether you have a match coming up etc...And if your're not on the game, then you have no idea what is happening... a simple notification on your facebook acc would be nice!! or better yet, if the person you've challenged does not accept then the match should be cancelled!
I think this is one aspect of the game that needs to be looked at.