Your perception checks can never be worse than your passive perception.
I am surprised that his comments on perception checks didn't light up the forum yet. At around 22:00 he starts talking about how passive perception is always working in the background to notice things. He goes on to say that your Passive Perception is always your floor for perception checks. If your passive perception is higher than the DC for noticing something, your passive perception always notices it. Perception checks are for noticing things that have a higher DC than your passive perception. He specifically says that if DM's are using passive perception correctly, then they will tell players about things that they would notice automatically, and use perception checks for a chance to roll higher than their passive perception. I have never played in a game that handled perception this way. It's always like this:
"I'm looking through the bookshelf for that book we were trying to find." [17 Passive Perception]
Give me a perception check.
"12"
You don't find it.
Then another character with a passive perception of 13 rolls a 15 and finds the book. What?
You know the general location of invisible creatures!
JC says that being invisible and being hidden are not the same thing. Invisible creatures give themselves away by making noise and interacting with the environment. Invisible creatures need to use stealth or have some other cover to be hidden. A monster or PC might be distracted or lose track of an invisible creature, but if you know someone is likely to be invisible and are trying to find it, you have a general idea where it is. He says that the game mechanics make invisibility awesome enough on their own - advantage on attacks, disadvantage on attacks against you, can't be targeted by spells that target "a creature you can see" - so invisibility does not need any additional benefits. I wish the DM who hammered away at us last weekend with the unseen, completely silent, unfindable shield guardian hadn't made us swing randomly at thin air until we got lucky and found it because he said invisibility made it impossible for us to know where it was.