I asked about this; sounds like it's a temporary thing that you just happened to notice. My guess is that it will be back on within a week or so.
Matt was right, it is now back a week or so later.
In fact, it is now improved. It now sports an alarm clock icon as well as supports showing multiple times for overlapping names such as current time in london:
I know a lot of people were upset when Google dropped this feature, so I am glad it is back.
Forum discussion at WebmasterWorld.