Not really. The defection rates in the 04 election were about the same as normal.
In 2004: 11% for the Dems, 7% for the Republicans.
Historic defection rates (from memory, so maybe not entirely accurate, but right around here): 10.5% for the Dems, 7% for Republicans.
We actually saw much higher defection rates in the 2000 election - only 86% of all Democrats voted for Gore, and 91% of all Republicans voted for Bush.
What is interesting is that the deflection rates for the Democrats could be enormous, if a recent Pew poll suggesting around 20% defection rates to McCain if Obama is the nominee is correct.