Gore got an eight point convention bounce in 2000.
Bush got a four point convention bounce in 2000.
After the Gore convention in 2000, the two candidates were statistically tied. Historically, the second convention's bounce is maintained much better than the first convention's bounce. In the 2000 case, the Gore convention bounce was maintained all the way to Election Day. The final tally was pretty much identical to the poll results three days after the DNC.
Not good news for Kerry.
Incumbents usually win unless the economy goes into a major depression. And a challenger usually has a unified party with an irresistable case for change pushing him forward. Neither of the latter things is true this year. Kerry's pushing a boulder up a mountain for all the good it will do him.