Unless you're using the Individual Summoned Monsters varient, then summoned monsters actually don't really exist in physical form until they're magic'd up.
Works like so:
A) I use a Conjuration (Summoning) spell to whistle up a Fiendish Orc. What I'm actually doing is getting a template copy of a Fiendish Orc from where ever it is that Fiendish Orcs come from in the outer planes - the Abyss, let's say. Essentially I'm using the photo negative from which all other Fiendish Orcs sprang to make myself a temporary magical servant. If the Fiendish Orc dies or when the spell's duration ends, that energy that I siphoned off to make my little buddy gets reabsorbed back into the pool from which it was originally drawn.
I use a Conjuration (Summoning) spell to get:
A Fiendish Orc.
B) I use a Conjuration (Calling) spell to transport to me and bind into my service Graanrak the Bloody-Handed, a Fiendish Orc with an overly impressive name. Depending on whether it's an arcane or a divine spell, I may have to prepare a binding circle to contain Graanrak, and once he's there bargain with him in order to gain his alegiance. Or, if it's a divine spell I don't even get to choose who is sent to help me - my god decides that Mr Bloody-Handed is just the orc I need to fix what needs fixin' and bammo, I get Graanrak on my side. The imporance here is that with a (Calling) spell, I -do- get a particular individual. If Graanrak has kids back in hell when Holy Joe Paladin smites Graany's teeth out thru the backside of his skull, all those little fiendish orc toddlers back home just suddenly became orphans. There's no pool that Graanrak returns to; he's dead, real and for true.
I use a Conjuration (Calling) spell to get:
Graanrak the Bloody-Handed, Fiendish Orc-About-Town
Now then, to point-by-point your individual questions -
So do summoned monsters all come from the Outer Planes?
Yes, all creatures from the Summon Monster line of spells come from the outer planes in some form or another. Summon Nature's Ally, by comparison, summons up prime material creatures and elementals, in the manner of A, above.
Are they regular sort of planar creatures going about their regular business?
See above. If you used a (Summoning) spell, then no. They didn't exist until you called them into being. If you used a (Calling) spell, then chances are that yeah, you just interrupted them while they were doing something. Which can just as easily be a bad thing (interrupting a vrock while he's watching his soap operas) as it can be a good thing (whisking that vrock away moments before he would be eatten by a bebelith).
If so, why are they not violently disoriented when you draw them to the Material Plane?
Again, above. If it's summoned, it didn't exist until you made it exist so there's no transition to throw it off-kilter. It shows up rarin' and ready to go. If it's called, it probably -is- disoriented and chilling in a binding circle while it gets its bearings (arcane), or your god gave it a tap on the shoulder in advance so that when it makes its transition, it's prepared for the trip (divine).
Does the magic of a summon spell somehow have a mind-control effect that instantly snaps them to attention so that they act immediately on the round you summon them?
Nope, but one isn't needed.
Do you always summon a pristine specimen ready to obey?
Summon - yes. Call - no guarentee. Arcane calling is taking a crap-shoot; it could be tip-top, or it could be hanging on to existance by a thread. Both situations have their advantages, as for instance, it's alot easier to negotiate with someone when they're mostly dead. Divine calling is much less risky. Face it, if the guy you're being sent isn't in peak condition, chances are he never would have been picked to help you in the first place.
