If I Unsummon a blocking creature will my attacker damage my opponent?

Question

Suppose Player 1 has a Dragon on the table and Unsummon in hand, while Player 2 has two Spiders on the table.

Player 1 chooses to attack with the Dragon and Player 2 chooses to block with one of the Spiders. Before damage has been put on the stack (Note: as of the 2010 MtG rules update, combat damage is a turn-based action that doesn't use the stack.) Player 1 uses Unsummon on the blocking Spider.

Does Player 2 take any life damage from the attacking Dragon?

Answer 1

No

The player takes no damage as the Dragon remains blocked. See the Compendium

509.1h An attacking creature with one or more creatures declared as blockers for it becomes a blocked creature; one with no creatures declared as blockers for it becomes an unblocked creature. This remains unchanged until the creature is removed from combat, an effect says that it becomes blocked or unblocked, or the combat phase ends, whichever comes first. A creature remains blocked even if all the creatures blocking it are removed from combat.

An Exception is, when the attacking creature has trample. See the Compendium

702.18c If an attacking creature with trample is blocked, but there are no creatures blocking it when damage is assigned, all its damage is assigned to the player or planeswalker it's attacking.