The short version of it is: the people willing to place their money where their mouths are are shying away from Guiliani. The overall picture is pretty much a muddle, essentially a five person race (including Ron Paul?!) with odds all centered about 5-to-1, or a 20% probability, ranging from 4-to-1 (25%) to 6-to-1 (17%).
Now... what does it really mean? In general, the "betting" sites offer a better picture of the race than the polls, because they're more forward-looking. However, they are subject to manipulation -- it's not necessarily that Ron Paul, for example, really has a 17% chance of winning, that's just the number at which they can draw an equal number of bets for and against.
It means that Fred is now the favorite at 4:1.
Rudy and McCain tied for 2nd at 5:1; Ron Paul at 6:1, Romney at 8:1. The Ron Paul odds show how subjective this is.