Google seems to be testing new font styles for the search results pages. Here is some screen shots of the current font that I see, followed by screen shots from some folks on Twitter noticing a new font style.

Here is what I see (click to enlarge):

Here is what @shemiadhikarath sees:

Here is what @jackalswitch79 sees:

Google is always testing, here is one more test that is ongoing.

Forum discussion at Twitter.