hi james,

these are the recent updates google did to its logarithm. it caused a lot of buzz because website owners who definitely didn't do anything wrong where thrown out of the index or put to the 10th page.
actually google does these updates to make it harder for you to cheat: they want quality content on their first positions and not over-optimized sites which don't deliver content for the visitors.

Google Panda is a change to the Google's search result ranking algorithm ..
Find its details here -- > Google Panda - Wikipedia, the free encyclopedia

Panda is the name/nickname of the engineer behind the algorithm update that is designed to improve the quality of search results; so they simple nicknamed the algorithm update "Panda".
The latest update is called "Penguin"...which is the worse update I have ever seen actually and well, why it's called Penguin I'm not quite sure of that yet! LOL