Carbides in the steel (especially those from overhardened sections such as from folding or wootz) give an "aggressive" edge which has microserrations making cuts easier. However, if you mean actual serrations on a blade, there are some problems:
1: Sharpening. How the heck do you do it? To get an effective cut (instead of a saw), you need not only the teeth to pierce, but the blade as well. That means every tooth would have to be sharpened not only on the tip, but on the edge as well. That would take an enormous amount of time.
2: Chipping/breaking. If you use a hacksaw, you will see that the teeth start breaking off after a while, especially when cutting steel. This is due to the fact that you have hard points with very little support. With a hacksaw, you can replace the blade. With a sword, that'll cost you ten grand. Ever wonder why kitchen knives aren't serrated? If you lose a tooth in your meat by levering on a bone, that's a real pain to get out and you may have to sacrifice your steak. Your bread knife, however, is serrated so you can saw through the loaf.
3: Serrations are difficult and expensive to make. The bread knife is the most expensive out of a set of knives for a reason. Now, try doing this over a two foot region on top of all the requirements for a normal sword. You are looking at a master smith to do this even partially well, and even using stock removal, it would take an inordinate amount of the smith's time.
Fencing Club at UH