Sneak Attack

When using sneak attack with weaponlike spells (i.e., damaging spells that require an attack roll), each individual attack is eligible for bonus sneak attack damage dice.

(Exception to the above: When using a spell that grants multiple attacks as part of the same action as casting the spell (such as scorching ray or desert fire), only one of those attacks is eligible for bonus sneak attack damage dice. The caster chooses which attack he wishes to use for sneak attack after making any attack rolls, choosing from those attacks which are both successful and qualify for sneak attack.)

Characters can sneak attack enemies who have concealment and other forms of miss chance (but still can't sneak attack enemies that have full concealment, or an equivalent level of miss chance).

Overrun

Ignore the Player's Handbook Errata on the overrun mechanics. Overrun works as written in the Player's Handbook; i.e. overrunning is possible as part of a charge.

Sunder

The rules for sundering a worn item now have an additional restriction. You cannot sunder an item that is well-secured, such as a ring or a bracelet, unless you have the target pinned (and even then, you suffer a −4 penalty on your attack roll). Items that are protected by armor (such as a ring protected by a gauntlet, or a necklace worn under an armor chestpiece) cannot be sundered at all.

Grapple

See the new size modifiers to grapple checks.