What is the most reliable World Clock Webservice that you use?
Here's a blog post which comes to the same conclusion.
Purists are quick to point to the accuracy problem. But I bet you could not even get perfectly accurate time even if your application was sitting on the same server as the atomic clock software itself.
I think there is a need for a clock Web Service. I can think of a few scenarios where it doesn't matter being off a few seconds.
Aside accuracy, another challenging area of serving up date and time is taking into account the daylight saving details of most country. That is something even the latest OSes struggle to get right. But that is definitely something that would make a clock Web Service valuable.