Suggestion for Leaver Penalty
Currently, part of the problem with the penalties offered for leavers is that they're easy to ignore. If you have a 20 minute penalty, you just start the queue, set a timer, and come back when the timer is almost over. You're not penalized at all if you know to start the queue before you actually want to play, regardless of how many games you need to do this for. The only real penalty is if you're playing multiple games in a row, and even then, it's easy to do other things in the interim.
Instead, the penalty should escalate to the following. After receiving the 20 minute penalty, the next penalty should be a 20 minute penalty, after which a random, undisclosed penalty that ranges from 0 to 60 minutes. This way, the user being penalized must be attentive to LoL the entire time, as leaving and having the queue pop while they're doing something else would start the process all over again. The user cannot ignore or avoid the penalty, but must actually endure it.