Different numbers of chromosomes?

I'm not a biologist, but...
one excellent example of this is that all the great apes except humans have 24 pairs of chromosomes, while we have 23 pair. Our chromosome 2, though, looks exactly like two great ape chromosomes fused end-to-end - it even has the remnants of a spare centromere and two telomeres in its middle. Yunis, et al, in Science, 208, 1145-1148 (1980) have very nice pictures of this, but they are also on the web somewhere - Internet Infidels discussion board for one place, with "Scigirl" (from Bozeman!) explaining them.
It seems pretty reasonable that a rare fusion event like this might not be a big obstacle to reproduction, either: unfused chromosomes from one gamete should pair right up with a fused version. It might get tricky when the zygote tried to divide, but hey - it only had to happen once.