Rand Fishkin spotted this subtle test by Google and posted it on Google+.
Google seems to be testing bolding the matching keywords to your search query in the title (clickable link) of the search results for users who are logged out but not for users who are logged in.
You can see in both cases, logged in and out, Google is showing the bolded keywords in the URL and description but not in the logged in titles.
Why? Everyone pretty much sees the same thing.
Forum discussion at Google+.
