The UPS Truck accident, occured due to an mechanical failure of the handbrake.
This event occured near Princeton, NJ.
The picture may have been taken on the 30.04.2004.
The man in the picture is Don Sheehy.

The picture, and modyfied versions may be found at flickr, digg.com,
4chan.org, pictureisunrelated.com, myspace, and motifake.com.
It can be found in various bloggs.
Possibly more places.

Sources (the 3rd link) indicates that it may not be Photoshopped, because the sewing machine does have a handle on the top, and the angle of the sun, and the shades of the other objects(i.e the UPS official and the cops in the background)is consistent.

It is funny, because it is kind of absurd.

There is also romours abot an seinfeld episode.
Including Newmans US mail Truck, and a sewing machine.

Everyone can make their own explanation of the event.

Links:

http://www.cs.cmu.edu/~dsheehy/index.html

http://www.dailyprincetonian.com/2004/05/03/10495

http://ask.metafilter.com/73484/Explain-the-unexplainable