Well...If you were a mathematician living in the pure world of statistics, with no physics, then yes, in an infinite universe there are in principle an INFINITE number of planets that look EXACTLY LIKE EARTH IN EVERY RESPECT. There are an infinite number of copies of you doing the same thing you are now doing!
I do not believe such simple minded extrapolations. Not only are they not testable and non-scientific, but quantum indeterminism and 'chaos' theory seem to guarantee that it is hard to get events to repeat themselves exactly because the universe is, at its root, not based on a strictly causal and computationally-finite set of laws. There may be many planets that look SIMILAR to our Earth, with oceans, a yellow sun, and life, but they would all be very different when you look at the details. Some would be 5 percent more massive, or 10 percent massive. The land masses would be differently shaped, the atmosphere would have settled on a different equilibrium composition, and so on. The Earth is unique, but at some level it looks like all the other planets orbiting sun-like stars at the same distance, and with about the same mass.
NOTE on October, 14 1996:
I just received a note from a mathematician who reminded be that even in an infinite universe, there need not be any duplications of the Earth at all. COnsider two infinite sequences, the numbers 1, 2, 3, etc and the squares of these numbers, 1, 4, 9 etc. Both are infinite sequences but they do not share all of the same elements! This means that the universe could be infinite in a mathematical sense, but not necessarily have an infinite number of repetitions of you sitting where are you are now, reading this note!