When did a bunch of old Un- cards get updated Oracle wordings? I just noticed it today on Rocket-Powered Turbo Slug. I know that for many years Un- cards didn't get Oracle updates at all; when did that change?

It happens when new Un-products come out.

"Yes, we had Rocket-Powered Turbo Slug and the Pacts, but there was a severe penalty for not paying off those debts." - I just realized Rocket-Powered Turbo Slug has the same functionality as the pacts. I looked at the release dates for Unhinged ('04) and Future Sight ('07), did the slug directly influence that cycle's creation?

Yes. The Pacts were directly inspired by the Turbo Slug.

Un-rules question: Rocket-Powered Turbo Slug's reminder text suggests that, unlike a Pact or Echo trigger, you are actually casting it as a spell the next turn. Does that mean it's a creature spell that can be countered while the creature is already on the battlefield?

The window to counter it is during the current turn not next turn.

Does Rocket-Powered Turbo Slug have haste?

It has “super haste”, which is haste plus, so yes it has haste. Things that care about haste do treat super haste as haste.

Are there examples of cards that got pulled from silver border into black border? (Aside from cheese stands alone)

The Pact cycle from Future Sight was based on Rocket-Powered Turbo Slug from Unhinged and the split cards were originally in Unglued 2, the Un-set that got cancelled.

Quicksilver vs The Flash vs The Roadrunner vs Sonic vs Rocket-Powered Turbo Slug?

The Silver Age Flash is the fastest of those listed.

Explain to me what super haste is?

Super haste (This may attack the turn before you play it. (You may put this card into play from your hand, tapped and attacking, during your declare attackers step. If you do, you lose the game at the end of your next turn unless you pay this card’s mana cost during that turn.)) From the card Rocket-Powered Turbo Slug from Unhinged. 

Unrules question. Two people are playing with no 4 of rule. Person A plays a deck made up of 60 Chancelor of the Dross while Person B plays a deck consisting of 60 Rocket-Powered Turbo Slug. Person A goes first. On their upkeep the Chancelors deal 21 damage, however the slug states it attacks the turn before it is played. Can the slugs attack before person A's upkeep?

No. They can only attack during its controller’s turn.

Am I the only one who thought of Rocket-Powered Turbo Slug when I saw the preview for that new Dreamworks movie, Turbo?

Nope. What Un-card she we push for the next big animated kids’ movie? : )

Can you attack with a Clone of a Rocket-Powered Turbo Slug the turn before you cast it? If so, do you have to pay 3R or 3U during your next turn (reminder text suggests 3R)? If 3R, is this a good way to get a Progenitor Mimic out cheap? If so, can you attack with the token copies the turn before they come into play? If so, do you have to pay their mana costs or not?

EDIT: I got this wrong the first time so let me get this correct. Superhaste is not haste. What it does is it allows you to put the card from your hand and attack with it the turn before you play it. By the time you can clone it, it is too late to be able to invoke the super haste. So, you spend 3U and get a red 3/1 with super haste, an ability you will not be able to use. You do not though have to spend 3R next turn.