If a GB is hit into a zone with a fielder and the batter is a Speed Demon, this is still a routine out, right?
If the base runner on 1st is a Speed Demon and the batter hits a GB into a zone with a fielder, the fielding manager can still use the fielder's choice rules to get a routine out at second, right?
If the base runner on 1st is a Speed Demon and the batter hits a GB into a gap, it requires a throwing attempt to get the out at second or a fielding attempt to get the out at first, right?
If the runner on 1st is a Speed Demon, the batter hits a GB into a gap, the fielder fails the throwing attempt to get the out at second, meaning the GB becomes a 1B, and the Speed Demon tries to advance an extra base, who has the ball?
I mean, who makes the throwing attempt to third?

1) Yes
2) Yes
3) Not completely clear, but I share your view. The fielder would need to make a throwing attempt to get the lead runner, or a fielding attempt to get the batter, However, since you don't declare what force out you want until after this check, it could go either way.
4) The outfielder in the same spray zone. Note that this is by logical extension, and not necessarily something I can back up in the rulebook.

If a GB is hit into a zone with a fielder and the batter is a Speed Demon, this is still a routine out, right?

Correct, this is a routine out. Since no fielding roll is required in this instance, the Speed Demon intangible does not apply.

If the base runner on 1st is a Speed Demon and the batter hits a GB into a zone with a fielder, the fielding manager can still use the fielder's choice rules to get a routine out at second, right?

Correct, the fielder's choice rules still allow the routine out to be recorded at second.

If the base runner on 1st is a Speed Demon and the batter hits a GB into a gap, it requires a throwing attempt to get the out at second or a fielding attempt to get the out at first, right?

Technically this is correct. The Speed Demon intangible is supposed to only apply to GB and Scorched GB results for the batter with the SD intangible (not a separate batter if the SD player is already on base) but the wording is not specific. Due to this, your example is mechanically correct given the current rules.

If the runner on 1st is a Speed Demon, the batter hits a GB into a gap, the fielder fails the throwing attempt to get the out at second, meaning the GB becomes a 1B, and the Speed Demon tries to advance an extra base, who has the ball? I mean, who makes the throwing attempt to third?

This is an excellent question, and I believe the distinction was edited out of the final rules. Here is the original ruling:

A failed throwing attempt is in the hands of the intended destination area. A failed throwing attempt that was supposed to be thrown to first is assumed to be at first, and the first baseman would then make the attempt. Similarly, if it is being thrown to second, the defensive manager should have declared whether the SS or 2B was going to be on the receiving end (in case a double play followed).

A failed fielding attempt, which becomes a 1B result, ends up in the outfield, in the same zone. An outfielder already in that zone becomes responsible for a subsequent throwing roll (if a runner takes an extra base, etc), otherwise, an outfielder must move into the zone to handle the ball.

I've added this to the FAQ list...

I agree with BH on the first 2.

From what I understand the SD ability that forces a throw on a fielding attempt only applies when the batter is a SD. If the runner is a SD and the batter is not, the fielder only needs to make a fielding attempt.

BH is right and I'm not sure if the rules state this either, however I can add something. During the chat the question was brought up about this happening and there being no outfielder in the zone where the GB went to. Basically the OF would move into the zone and get the ball to make any necessary throwing attempt. The OF that moved into the zone DOES NOT give the runner a +1 to his speed because of moving.

correct -- because that modifier assumes an immediate reaction/move to the ball... when the ball is hit and a fielding/throwing check is failed, everyone else on the diamond is not just sitting around watching -- fielders are moving into position to back up a play, etc.

So the only time the SD intangible can be used on a regular GB is when the fielder has to move to the zone where the ball was hit? I see it as everytime a regualr GB/GB Scorcher is rolled you make the throwing attempt. It would be like a slow roller to the SS and a fast throw has to be made to get the batter out or the batter diving into first for the base hit.

The rules state:

I think the key phrase is "instead of a fielding attempt". If there is no fielding attempt required (i.e. a routine play), then there is no throwing attempt and the batter is out.

I agree that it is unclear and could be read another way. But the way that I see it, nothing trumps routine outs. A routine play is always an out. A bit OT, but if you note that under the rules for players playing out of position it states,

Here players OOP can't make routine plays, so they must roll.

Doesnt it say that a throwing attempt is needed IN ADDITION to a fielding attempt?

Hehe, no. I cut and paste that directly from the rules.