Last week was the Semantic Desktop hands-on workshop in Berlin, and Leo's video really says almost everything. I found the format of the workshop (morning talks, afternoon free time) really nice, as I can't really pay attention for a whole day.
On the train to Berlin I had lots of laptop battery and I tried to brain-storm something quick and dirty I could hack up using machine-learning, I wasn't very successful.
HOWEVER, I remembered an interesting idea by (I think) DJ McCloskey at the IBM language-ware labs: The email radar! Imagine the motion detector from Aliens, but showing the unread/unprocessed emails in your inbox. More important emails/tasks appear as bigger dots, this would give you instant overview of your day and how stressed you should be. Or alternatively, when you should just give in and lie down to die. Then the idea spirals out of control a bit and you can imagine "ENEMY DESTROYED!" sound effects and explosions when you mark something as done or file away the email.
From this the idea of Semantic Space Invaders! was born:
Fly backwards in time and destroy your flickr-photos!
My original idea was that this could combine your various RSS feeds to let you destroy your activities over the last few weeks, however, technical difficulties meant that only flickr was supported (parsed really badly so it might break). Also, it's harder to come up with nice icons for other RSS feeds, although I was briefly thinking about finding a service for creating web-thumbnails.
Another nice feature that I would implement if I had infinite time is to auto-compress the timeline in periods where there is no activity.
Like last years rdfroom this is written in python using pygame.
(Oh and btw, yes, this IS completely pointless, but it only took me a 2-3 hours :)