Prior Presidents didn't use signing statements even a fraction as often as Bush does. 750 to date for W, vs <200 for Clinton, and used more aggressively. Interestingly, now-Justice Alioto first proposed expanded use of signing statements during the Reagan Administration, so there's at least one Justice who might think these statements actually have any legal effect. There otherwise isn't much support for the idea that these statements have meaning.
http://en.wikipedia.org/wiki/Signing_statement