If a monster's Summon is negated, it is neither sent from the hand nor the field to the Graveyard. So if the Normal Summon or Flip Summon of "Sangan" is negated, it will not be able to activate its effect because it was sent from 'nowhere' to the Graveyard, not from the field to the Graveyard.
Since the monsters in limbo are not considered to be face-up on the field, if they have a Continuous Effect, it is not applied at the time. So if "Jinzo" is Normal Summoned, "Solemn Judgment" can be activated to negate the Summon. This goes for Spell and Trap cards as well.
With the introduction of Xyz Monsters, 'Limbo' has unofficially been used to describe the state in which Xyz Materials exist, as they are neither on the field, nor in the graveyard. Entering 'Limbo' from the field does not count as leaving the field. Entering the Graveyard from 'Limbo' does not count as leaving the field either.
In the source code of Yu-Gi-Oh! BAM, during battle, along with usual terms found in that game such as "Attack", "Boost", "Immunity", "Death", "Negative Boost" and "Effect Trigger", the term "Limbo State" can also be found.