
Rather than taking these claims at face value (especially since most were just comments on blogs or videos, with no effort to back them up with research), I decided to take on the task of doing some research myself. I would examine the stories of these other gods that the Jesus story is said to have been stolen from, and come to my own conclusions.

Case Study: Jesus vs. Horus
Comparisons:
Birth:
Jesus: Born of a virgin named Mary, who was impregnated by the God / the Holy Spirit.
Horus: Born of the Goddess Isis, who reconstructed the body of her dismembered husband Osiris so that they could conceive their god-son Horus. Isis was not a virgin, since she was in fact sexed up by the golden phallus that she made for her husband Osiris. Both Horus' parents were gods.

Jesus the Christ: means Jesus "the anointed one". Taken from the Hebrew ritual of anointing someone with oil so that they have a divine purpose or influence.
Horus: means Falcon, other meanings include variations of "the sky" or "the one from above".
Death / Resurrection:
Jesus: Died after being crucifed, was resurrected only once as the same man, Jesus. He remained on earth for 40 days before ascending into the heavens.
Horus: Died and was continually re-incarnated as each successive Pharaoh. Horus is considered the Pharaoh and ruler of both the world of the living and the dead. I didn't find details relating to how Horus died.
Entity:
Jesus: God in human form.
Horus: He was said to have been the sky, and also the sun and moon. The sun and moon were his eyes, and when these celestial objects were seen traveling across the sky, it was said to be Horus, the falcon, flying across it.

Jesus: Allegedly looked like any other financially poor male from the period, probably having long-ish hair, a beard, and the common robes of the common man. Was a Hebrew from the middle-east, so was probably of dark complexion, dark hair, brown eyes (as opposed to the oft-depicted light-skinned, blonde, blue-eyed Jesus).

Enemies:
Jesus: Usually enemies involved people of power: royalty, the Pharisees, etc. This was mainly because of Jesus' claim to being the song of God, which was a heresy (unless of course you actually WERE the son of God, which then of course anything goes).
Horus: Many stories show Horus' jealous uncle Set (the god of the desert) to be a prevalent enemy. Many battles between the two are told, some for Horus to avenge his murdered father Osiris, and others to fight for the rule of Egypt.
Theological Hierarchy:
Jesus: The same entity as God and the Holy Spirit. None seem to have any authority over the other, as they all are facets of the same God. Jesus does pray to his "Father" many times which could indicate Jesus' lesser status as God, however in many cases this is said to have been done as an example to other people witnessing the prayer. Other prayers by Jesus are also said to have been strictly fulfilling prophecies made by previously written scriptures.
Horus: Seemed to be somewhat of equal powers/abilities/authority as his uncle Set, whom he battled and challenged in many different ways (from actual fights to boat races). The two go before other apparently higher gods to argue over the rule of Egypt.

Jesus: was a human child in his youth. Not much is mentioned about specific clothing or adornments.
Horus: Was thought of as the form of the rising sun, supposedly representing the first light of day. Sometimes depicted as a human child wearing the united crowns of Egypt.
As Savior:
Jesus: the savior of all humankind, providing the only way into heaven after your physical body dies.
Horus: referred to as savior with respect to rescuing his father Osiris' earthly domain from Isis' brother Set. Possibly other reasons for the word "savior", but none seem to point specifically to the salvation of man in any way.
Purpose as a God:

Horus: I can't seem to locate any specific purpose for Horus' existence as a God, nor any specific reward or punishment for worshipping him. The gods of Egypt, much like the gods of Greece, seemed to procreate at will and for no specific divine reason, just like people do. If anyone has more sources on this, that would be appreciated.
Relating to other Gods:
Jesus: Is the same as God and the Holy Spirit. Considered one of three facets of the same God. Said to be the only one true god.
Horus: Very closely associated/intermingled with many other gods, including: Re (god of the sun), Min (god of fertility), Sopedu (some sort of protecting or "border-patrol" type god), Khonsu (god of the moon, time and knowledge), and Montu (another god of the sun, also a warrior god).
I'm trying to stay unbiased here, but I have to seriously say WOW... how could anyone on earth actually think these two stories are even remotely related? I think what happens is someone reads a claim online about this (or watches Zeitgeist), and then just spouts it out to everyone they know without actually doing the research. About an hour of research tells me pretty quickly that there doesn't seem to be any plagiarism of any kind between Jesus and Horus. The two stories are very unique from each other. But hey, do the research yourself, that's the only way to know anything for sure anyway.