What we concieve as infinite is interesting, because even if there is an end to the universe, like, would you bump into a wall or something? What defines that ending? But to throw in my opinion, I believe that the universe is infinite, but not quite how you might think. Here's my theory:
The big bang created a large outburst of energy that is still raging, and, theoretically, getting bigger harder faster stronger every day. Where there is matter, or some sort of magnetic, gravitational, or whatever it might be, field, some sort of energy, this is what we think of as the universe. Beyond this is an infinite stretch of absolute zero. (
http://en.wikipedia.org/wiki/Absolute_zero)
What is in this field of still, cold, no energy stretch is also a mystery, for all we know there may actually be multiple big bangs, that you could think of how you think of galaxies, but on a MUCH grander scale. If this is true, there would be no possible way that you could actually reach these other masses and onsets from big bangs, which would literally classify them as other universes.