I reported gingernorks post, but it probably didn't contravene MN rules. I had seen comments elsewhere about this episode but I would never have posted anything here about it before it had aired in the UK.
Generally, the "rules" about spoilers on the internet is that if a forum/newsgroup is global, then comments on episodes can be made as soon as it's aired in whatever country it's first aired in. If a forum/newsgroup is mostly local to one geographical area, then comments aren't made until that episode has aired in that area.
This courtesy thing is a bit fuzzy, especially as MN has members from many different countries, but the vast majority (I'm pretty sure) will be resident in areas where the latest episode has not yet been shown.
In newsgroups, generally only the topic title is visible, and you have to physically click on that to show posts. But on MN, if you use the "last 15 minutes" etc options, a spoiler could show up on the screen and then you don't have any choice as to whether you read that spoiler or not.
But, I've been around the internet for a long, long time, so I've pretty much absorbed the "rules" about spoilers and why they are there. (And seen squillions of arguments on the subject.)