We all love to see new footage from our most hyped upcoming games. Once we've found said footage, we just can't help but share it with our Wii loving bretherin. This is the best decision, of course. After all, why would people not want to see new footage?
Here is the reason they wouldn't: SPOILERS. Spoilers can be screenshots, representational texts or videos that feature an important plot detail or elaborate on an announced but mysterious feature that's implemented into a game. I've seen alot of people leaving boards where they have 14,000+ posts forever because they saw a screenshot of Gannondorf from Twilight Princess.
Basically, if it's new and it features something major that happens in the game then you can still feel free to show it, but you should put *SPOILERS* in the title. So, say we find out that Tingle from the Zelda series was in Smash Bros Brawl. We couldn't just say "Tingle is in SSBB". We'd have to instead say "*Spoiler* New character in SSBB". This way we can avoid confrontation or upsetting people.
Please follow these rules.