Am I sure? Maybe 85%. There's no official, well spelled out, instructions with examples.
The official rules are that during the upkeep you make decisions affecting your own objects, and if there's a timing issue the player with Initiative decides. That's pretty much all that's written.
The examples I gave assume that the player with Initiative cares about the order of everything that he possibly can, so he or she gets to decide it all.
It's not nearly as powerful as it looks, though. Nearly all abilities that occur in the upkeep only effect one player's objects, or effect them with individualized events, so that no single event affects more than one object.
Burns, all curses except for Death Link, Regeneration, Upkeep +X except for Mind Control, etc all create single object events.
There's some rules ambiguity about which cards exactly qualify, but off the top of my head, it's mostly only two categories of cards. Idol of Pestilence / Altar of Skulls and that sort of thing on the one hand, and Enchantments with Upkeep +X and a secondary effect like Force Crush on the other. And even with Force Crush, you can't do the damage before you pay the mana because of the way the card is worded.
Force Crush is actually an interesting corner case, because it may not qualify. Normally, the controler of Force Crush would be the one who decides when to pay Force Crush's Upkeep cost. It's not clear if the damage is a new event that the creature's controller must order, or if it's part of the same event, which would cause a timing conflict and be reaolved by Initiative.
Now that I think about it, being conditional like that probably means that Force Crush's controler is the only player who decides when to pay the upkeep, and the damage is added to the event too late for it to matter in the ordering of events.
So there you go. Not even Force Crush counts.
I do know that it matters for Skeelax, Taunting Imp, because if the flame is on an opponent's creature it might go out before Imp has a chance to regenerate.
Really, though, there aren't that many times when it matters. Most players probably never have it come up. You've played this far without worrying about it, right?