speechwatch

A wristwatch, like any other, except: Voice activated scheduler.

The watch contains a standard voice recognition processor (Atmel, et al sell processors with voice recognition and small dictionaries built in), microphone and speaker.

The watch would recognize a few words, such as "in", "remind", "days", "hours", "minutes", the days of the week, months, etc.

The processor would recognize several types of request, such as:
"in 5 days remind me to pay my bills".

The voice recognition part would look at the part "in 5 days remind me to". It would parse the 5 days part, and add an entry into a database which would trigger in 5 days. The "remind me to" part would trigger a recording function, which would record your voice and dump the sound into an audio file. In 5 days, it will play the audio file back.
This way, it doesn't have to know what "pay the bills" means, you simply hear yourself say it in 5 days.

Other phrases include:
"in 2 hours remind me to...."
"What is happening in 1 week" - would play back anything that occurs in 1 week, etc.
use your imagination.

Since there would be chance for background noise/annoying co-workers to add things to your watch, a button press would define when it was "listening" for commands, and letting go would signal when you were done adding an entry (since it doesn't recognize the words in the entry). This would also make it more feasible battery-wise, since it wouldn't constantly be recording and checking for key phrases.

Additional features could include the ability to check for collisions - i.e. if you are adding an event in close proximity to another, it could point out that you already have something scheduled at that time, and ask if the events can be put in to occur simultaneously.

For things that take prearranged amounts of time, you could say "on december 12th, 3pm until 4 pm exclusive, remind me to go to the widget meeting".
The exclusive part would force it to prevent any collisions with other activities, such as "play with my kids" or "visit parents in home"

The watch will also synch with your computer to provide a more visual calendar when desired.

Possible problems include battery life and speaker volume. A small vibrator might need to be included, like in a cell phone, for optional noisy environment notification (side feature: it listens to ambient noise to decide whether or not to trigger the vibrator). A "repeat that last message" button would be necessary.