Hmm, never thought about that before. Found a short discussion of it here. I'm inclined to agree with Claxon that companions only go along on one teleport, the first, but it's arguable. I'm pretty sure they don't appear only at your last appearance, because something might kill you along the way (like somebody with Teleport Tactician) and then where would your companion be?
Also never thought of that. I think the simplest answer, and one that many GMs might be tempted to adopt, is that it's simply a special modification of the spell or ability that doesn't let you take anyone along for the ride. Not really a satisfying answer though.
Per RAW, in a normal Dimension Door spell, the additional ally or allies would be dropped off wherever the teleport effect ends.
You instantly transfer yourself from your current location to any other spot within range. You always arrive at exactly the spot desired – whether by simply visualizing the area or by stating direction. After using this spell, you can’t take any other actions until your next turn. You can bring along objects as long as their weight doesn’t exceed your maximum load. You may also bring one additional willing Medium or smaller creature (carrying gear or objects up to its maximum load) or its equivalent per three caster levels. A Large creature counts as two Medium creatures, a Huge creature counts as two Large creatures, and so forth. All creatures to be transported must be in contact with one another, and at least one of those creatures must be in contact with you.
If you arrive in a place that is already occupied by a solid body, you and each creature traveling with you take 1d6 points of damage and are shunted to a random open space on a suitable surface within 100 feet of the intended location.
If there is no free space within 100 feet, you and each creature traveling with you take an additional 2d6 points of damage and are shunted to a free space within 1,000 feet. If there is no free space within 1,000 feet, you and each creature traveling with you take an additional 4d6 points of damage and the spell simply fails.
Dimensional Dervish
You teleport with a mere thought, savaging your opponents as you flash in and out of reality.
Prerequisites: Ability to use the abundant step class feature or cast dimension door, Dimensional Agility, Dimensional Assault, base attack bonus +6.
Benefit: You can take a full-attack action, activating abundant step or casting dimension door as a swift action. If you do, you can teleport up to twice your speed (up to the maximum distance allowed by the spell or ability), dividing this teleportation into increments you use before your first attack, between each attack, and after your last attack. You must teleport at least 5 feet each time you teleport.
Special: A monk can use additional points from his ki pool to increase his speed before determining the total speed for this teleportation.
In a Dimensional Dervish, only one teleportation spell is being used but it is divided into increments, so it's one teleport spell, not several, so the "end" of the actual teleportation spell is wherever you end your round to deliver the last attack.
This is how I read it RAW.
I have a PC in a Gestalt Campaign who uses Dimensional Dervish, and we agreed that he could not drop them off wherever he wanted even though he argued that each individual teleport effect is it's own teleport. So here's the possible abuse: If you take 4 people with you, you can teleport, drop someone off and strike, teleport again and drop someone off and strike again, and teleport again and drop someone off and strike, and then teleport a last time and drop someone off and strike. You could theoretically teleport to 4 different locations within the range of the teleport spell (so 1200 ft max), dropping your 4 allies off at each individual location, and it could be additionally argued that if each teleport spell is it's own teleport effect, you could theoretically go pick them back up in the same manner. And if you have multiple Dimension Doors prepared, or if you're a spontaneous caster, you can do this all day.
It's abusive and it's a nightmare to do it any other way than you teleport your whole group with you until the spell ends.