I had to say this within the first couple of weeks of the league's formation, and hoped I hadn't the need to say it again, but here it goes.
If someone messages you or invites you, SEND THEM BACK A MESSAGE, WHETHER YOU'RE GOING TO PLAY THEM OR NOT. THIS IS COMMON COURTESY.
If someone asks you to play, then they're going to sit around until they know if they're playing or not, or think that you're ignoring them.
If you leave your xbox on in-game, then CHECK TO SEE IF PEOPLE MESSAGE YOU. It isn't difficult to walk over to your xbox, and push one button to pull up the guide and check for messages. If you don't have the time to look at a single message and type out "I can't play right now", then you don't have the time for a 2-day sim period league. If you're temporarily indisposed, then set yourself as away.
I've been hearing a lot of complaints about this lately and many of you may have seen a couple of posts on it. Don't make me have to start booting people because they're too lazy to type out one sentence.