The results from Timex' future-vision design contest are pending, but here's my idea of a timekeeping device for the year 2154: (Unfortunately I couldn't enter due to the demands of my move at the time of the deadline.)

150 years out says beyond wearable to me: think Cortical Implants with the ability to virtually project information overlayed with your regular vision:

Now combine the state of the art in time shifting technologies with virtual graphic overlays and imagine a system that would allow you to "see" time based information such as milestone markers virtually overlayed with the real world:

Ghost Data would represent realtime splits of your past performance or famous races or events.

(Let's load that Carl Lewis program again but timeshift it to 50% this time so I have a chance!)

This type of concept could eventually replace numerical representation of time with information about the meaning of time itself.