Problems with Laplace's Demon?

Pierre LaPlace proposed a theoretical method of being able to know the entire past and future of the universe (linky). If you knew the position and velocity of every particle in the universe, then you would be able to calculate where each particle was headed, along with where each particle came from. In a macro sense, it’s the same idea behind simple temporal deduction: if you’re running at me at 5 miles an hour, and no forces have intervened, then I know exactly where you were an hour ago.\

This is a very old theory, however, and it works best in a simple Newtonian context. I’ve read that this method of calculation breaks down when you add entropy to the mix, as information is lost in thermodynamic interactions. But while chaotic, knowledge of every particle’s position and momentum would still let you figure out the past and future, right? It’d just be a lot more number crunching. Can the idea be debunked with thermodynamics alone?

Also, here’s a wikipedia quote that seemingly puts a nail in the whole idea: There has recently been proposed a limit on the computational power of the universe, i.e. the ability of Laplace’s Demon to process an infinite amount of information. The limit is based on the maximum entropy of the universe, the speed of light, and the minimum amount of time taken to move information across the Planck length, and the figure was shown to be about 10^120 bits.