Teleportation, Summoning and Calling spells and abilities (anything that involves a brief travel through the Astral Plane, really) have a random chance of working properly or cause the targets of the spell to briefly travel through an inner plane connected to the negative energy plane with less than healthy results: I'll roll 1d6, 1 = normal travel, 2 = through the negative energy plane (fort DC 25 or get 1 negative level), 3 = through the quasielemental plane of Vacuum (fort DC 25 to avoid 3d6 damage as your lungs implode), 4 = through Dust (fort DC 25 to avoid 1d6 CON damage and 1d6 rounds of stunning due to sneezing and choking), 5 = through Ash (2d6 cold damage, no save), 6 = through Salt (2d6 damage from dehydration, no save). Astral Projection or similar spells have a similar chance to bring the targets to such an Inner Plane instead of the Astral Plane. As a result, most fiends avoid using their teleportation and summoning abilities while in the Material Plane, unless they're really in dire need.
Spells with the Evil descriptor function at +2 caster level.
Spells with the Good descriptor are impeded (you have to succeed at a DC 20+spell level concentration check or lose the spell).
Spells and spell-like abilities that use negative energy function at +2 caster level. Class abilities that use negative energy, such as channel negative energy, gain a +4 bonus to the save DC to resist the ability.
Spells and spell-like abilities that use positive energy (including cure spells) are impeded (you have to succeed at a DC 20+spell level concentration check or lose the spell). Characters on this plane take a –10 penalty on saving throws made to remove negative levels bestowed by an energy drain attack.
The Material Plane is now strongly Evil Aligned, so a –2 circumstance penalty applies on all Intelligence-, Wisdom-, and Charisma-based checks made by all non-evil creatures.
The spell Planar Adaptation can be used to avoid these environmental effects, even if you're native of the Prime, but it won't stop teleportation mishaps, unless you also use Planar Adaptation with regards to the Negative Energy Plane and the Quasielemental Planes.
