Sneaking up on people

[Andezzar]

This is only a RAW discussion, I do not intend to rule it like that as a GM.

Am I missing something or is it impossible to sneak up on people unless the target cannot see the sneaker (sneaker invisible, darkness, etc.) or you are using the optional facing rules?

According to the SRD "You need cover or concealment in order to attempt a Hide check".

So if the target stands 5 ft. square away from cover the sneaker cannot reach him undetected.
Also according to the SRD "If people are observing you, even casually, you can’t hide." Since the target does not have a limited FOV without the facing rules, he should be able to see all around him, making sneaking up impossible.

[Curmudgeon]

Yes, you're missing at least a couple of somethings here.

One important consideration is the good (generally Supernatural) forms of Hide in Plain Sight, which remove the requirement for cover/concealment. Sneaking up on someone is then usually just a matter of having a superior Hide skill. Even the shadow of a single blade of grass 10' away is enough to let a Shadowdancer or Assassin sneak up on you; that's why it's Supernatural (magical). This is a powerful ability which gives non-spellcasters a big leg up. True Seeing can't do anything against a good Hide check. (The magical part ─ Hide in Plain Sight ─ only happens on the sneaker's turn, and the Hide check which it enables isn't magical at all.)

For even more purely mundane sneaking, Complete Adventurer (pages 101-102) has rules to Move between Cover. Basically you can move up to your Hide ranks in feet away from cover/concealment and still make a Hide check.

This is only a RAW discussion, I do not intend to rule it like that as a GM. I strongly encourage you to try the RAW approach first. With clever players who know the relevant rules you'll find quite a lot of sneaking will take place.

[Leon]

Even the shadow of a single blade of grass 10' away is enough to let a Shadowdancer or Assassin sneak up on you

A veritable clown car for Ninja to spring from

[Andezzar]

I know about some of the ways to avoid the problems. What irks me is the RAW 360° field of vision. Also I cannot find in the rules how long a successful hide check is supposed to last.

You cannot start hiding if you have total concealment from the target, like when you are still in another room. You could stat hiding when you are standing near the doorway, but the rules do not say when you can no longer hide. Is it immediately after going through the doorway (no more cover)? Is it only after moving up to half your speed (or more with the appropriate penalty)? Can you remain hidden indefinitely after the successful check regardless of the lack of cover/concealment?

[Doorhandle]

Only if they're ninja contortionists.

They can only all hide there if they FIT, remember.

[Curmudgeon]

Also I cannot find in the rules how long a successful hide check is supposed to last.
It's an opposed check, so it's good for the round in which both characters make those rolls. However, there's also this to consider:
Action: Varies. Every time you have a chance to spot something in a reactive manner you can make a Spot check without using an action. Trying to spot something you failed to see previously is a move action. There's a lot of DM discretion possible in that "something" term. Depending on which side of the Spot/Hide balance they favor, it could be any of the following:

a character or object
a character or object in the same place
a character or object in the same place, doing (or not doing) the same thing
If it's the first option, one successful Hide check means the Spotter has to use move action retries to ever see you (and the Quick Reconnoiter feat in Complete Adventurer is much more valuable). If it's the last option, doing anything differently from round to round is a new situation for the Spotter to react to without needing an action.