Nate Silver crunches the numbers. The gist:
A 6-point convention bounce represents par. If a candidate gets a bounce larger than 6 points, that can be considered to be a good sign. If the bounce is smaller than 6 points, that can be considered to be a bad sign.
This article available online at:
http://www.theatlantic.com/daily-dish/archive/2008/08/what-a-convention-bounce-looks-like/212943/
