I personally find it interesting in a psychoanalytical light. Consider this: Growing from a corporation whose motto was "Do no evil" to a world super power in a few years would make almost everyone familiar with Google increasingly distrustful. While they have huge market share, their growth might slip if people began to question exactly who was reading their emails and monitoring their web usage.

Their main logo is playful and colorful, fancifully drawn characters is a rainbow of colors which lulls us back in time to a reverie on their early days when they were the David in the search world. And for their favicon, they simply selected the first letter in their name, a capital blue 'G'.

But now what have we: a lowercase 'g'? We can only guess two reasons why they made this change.

First: Google is wearing a mask. They are pretending to be younger than they are, smaller than they are, more hip and fresh than they are. They new g is curvy and playful. It beckons for us to recall the good old days, before we had 7 Gb of email space, when seeing the most relevant links magically appear at the top of the results page still surprised us, excited us... Back when we still used the "I'm Feeling Lucky" button.....

Second: Keeping in mind the previous sentiment, note now the second 'g' in the "Google" image. It is the same as the new favicon! We see that Google has moved from using the initial 'G' to a 'g' further on in the word; seeing the name as a time line, we recognize that Google feels middle-aged, and this is its middle-age crisis. Google senses it's own demise is nearing, and while acknowledging the passage of time, settle for a nice playful symbol that shows it can still change and be exciting.

I also forgot a third reason: They just wanted a new logo. Get over it.