Are Long URLs bad for SEO?

In his PC Magazine article SEO Fiascoes: The Trouble With Search Engine Optimization, John C. Dvorak postulates that long URLs are detrimental to SEO, despite what everyone else seems to be saying.

He conducts an experiment on his own 1.2 million page views per month blog by changing existing URLs to the long version, and sees an immediate drop to 900,000 page views.  Dvorak sites this as proof that it doesn’t work.

I can’t help thinking that the drop is due to the search engines dropping the old URLs and re-indexing the long URLs. This takes time. Maybe if Dvorak reviews his page views in a couple of months he’ll see a different picture.

What do you think?