A Google statement released on their official blog has announced their latest round of updates, called caffeine.

"For the last several months, a large team of Googlers has been working on a secret project: a next-generation architecture for Google's web search. It's the first step in a process that will let us push the envelope on size, indexing speed, accuracy, comprehensiveness and other dimensions."

Matt Cutts has done the rounds with interviews and put up some further information on his blog. So far we have been told that the changes are under the hood so nothing will look different and that this has been worked on for about 2 years. Presumably, more will come out in time to come. Matt has said,

"Most of the search result rankings should be the same, because what’s changing is infrastructure under the hood of the search engine. But Caffeine is a radical revamp (more like a complete rewrite) of large parts of our system, so not all the rankings will be unchanged."

More as we get it.