|This block has not been implemented.
The spike block was just said to be a good idea by Jeb. Whether or not he is working on it or intends to include it is player speculation.
Spike Blocks are blocks originally planned to be introduced instead of Sticky Pistons. They would work like pistons but push out Spikes. It was later suggested to Jeb that he should make Sticky Pistons instead and also make a Spike Block that could be pushed by them.
On May 28, 2012, Dinnerbone stated he wishes to add Spikes to Minecraft, but is unsure how to implement them.