Is there a limit to the number of names you can give someone?

I have two Hebrew names. One of my sons has 3. Many people I know have 3; someone I called to the Torah had 4. At 3, people who have to address you often, (rebbes, teachers) seem to get confused. (can't quite explain why this would be worse than rembering the names of the other 25 in the class, but that's what it seems to be.)

Is there a limit to the number of names? If so, what is it, and why this limit?