Just a few rules to live by when posting spoilers on The Smallville Message Board:
A SPOILER is a post that contains information about what happened on the most recent Smallville episode. This is because not everybody gets to see Smallville on Thursdays at 8 pm due to various reasons. This SPOILER rule is to protect them.
The episode is officially considered in SPOILER mode from the first minute it airs and lasts for TWO WEEKS or until the next new episode airs (which ever comes first). Once this period is done, you can discuss the episode or stuff that happened there without using "SPOILER."
Promos for next week's show are covered under the above rule.
An EXTREME SPOILER is any information about a show that has not been aired yet. The only exception is the promos, and that's because promos are, technically, already aired. If you know what's going to happen with a certain character a few episodes down the road, you must include EXTREME SPOILER. Even if the episode is going to air in 5 minutes, you must include EXTREME SPOILER.
Also, when making a subject heading, do NOT include the spoiler in the title! A post titled "Whitney -- EXTREME SPOILERS" would get deleted immediately. Whitney isn't on the show right now (thank god!). Therefore, the mere fact that you're telling us there's an extreme spoiler about Whitney automatically tells us that Whitney *will* be on the show. That's an extreme spoiler in itself. Merely say something like "Episode 17 -- EXTREME SPOILERS" so people who want to be spoiled can check it out, and those who don't can avoid it.
And yes, casting information is considered EXTREME SPOILER.
Any posts that include SPOILERS or EXTREME SPOILERS but doesn't have the proper warning will be deleted.
So, basically ...
Before the show airs = EXTREME SPOILER.
After the show airs = SPOILER.