Looking back one, two and five years ago today on Worldchanging:

2009
Bike Safer, Bike Smarter, BikeWise
To help make biking safer we need to make it smarter. Enter Bikewise, a new collaborative information site where bike commuters can enter reports about thefts, crashes and hazards...

2008
Nothing for today!

2005
What Does Peak Oil Look Like?
James Cascio looks the "Peak Oil" conversation; he provides a useful visual companion to the peak oil argument via Green Car Congress and links to political blogger Kevin Drum's three-part series of posts that go into more detail about peak oil arguments, while avoiding the energy industry jargon that often infects them...

Other recent "look backs":
May 27
May 28
May 31