I never really gave Tumblr much thought, but I recently have started a couple side projects and I've found the service a great way to toss a well-put-together blog in very little time. For instance, I just started a new one called "Ahead Of Yesterday".
I've seen several people do those pictures-a-day projects and was interested in doing something similar. I was fascinated how that simple series of pictures forced the people I know to pay more attention to their surroundings, looking for all the not-so-hidden scenes they might not have otherwise noticed. Also, it acted as a metronome, with each picture indicating the passage of time.
Taking this literally, I've decided to post one picture a day, starting on my thirty-fifth birthday. Each picture would be of a number, with that number increasing for each day. So on my birthday, I took a picture of the number "1", the following day I took a picture of the number "2", etc.
This purifies the original idea, forcing me to look up and around more often than I'm used to, encourages me to take alternate routes in search for the next number, be choosy about design aesthetics if presented with multiple options, and makes me intrinsically aware of time passing by, counting the days I stay ahead of yesterday.