Gorilla/Orangutan Hybrid

[Roboramma]

I understand that part. My main question was regarding the fact that at some point the 48 chromosomes permenantly became 46 (at least in the "human" branch). In order for the offspring not to be sterile, both parents would need to already have the fused chromosomes, so that both had 46. Am I correct in assuming that, or am I missing something? It's been 10 years since I've been in a biology class.

I don't think the offspring will necessarily be sterile. Actually there was another thread recently about the idea of human-chimp hybrids, and this same question came up. I might be misremembering but at that time I think someone said that some mules aren't sterile. This is backed up very slightly by a quick google which turned this page up, which says "Mules are almost always sterile." Implying that they sometimes aren't.
Horses and Donkeys have a different number of chromosomes.

The fact that mules sometimes aren't sterile suggests to me that at the time of the event that resulted in a different number of chromosomes, sterility was even less likely than it is now - after all, the rest of the genome would still have been pretty similar.

Okay, so the second generation had to have brother & sister as mother & father. Stranger things happen in modern society. Aren't we all descendants of "Eve", as shown by mitochondrial genetics?

The "Eve" thing is a bit misleading. Yes, we all have a most-recent common ancestor on the female only line (you're mother's grandmother's grandmother's grandmother's...for a long time... grandmother).
However, she was still a member of a population of humans (they were likely already homo sapiens if I remember the timeframe right), many of whom were also your ancestors, just not ancestors to all of the people alive today - though many of them might have been (just not along the female only line). Certainly her decendents were no more likely to be inbred than anyone else's.

She wasn't a lone woman, or really special in any way. She wasn't different from the other people living with her, or those in other parts of the world, or those who lives shortly before or after her (on an evolutionary definition of shortly).
In fact, since she's defined by those currently living, a completley different woman from a completely different time might become "eve" if the right people died off.
To illustrate this with an extreme, if all of humanity except your family died off, your mother would be mitochondrial eve in just the same way that this prehistoric woman is/was (I think "is" is more correct, for just the reason that I'm talking about - she's defined by the present not the past).

 

[Soapy Sam]

Most likely impossible.
Orangutans are not even in the same family as gorillas, chimps, bonobos, and humans. Phylogenetically, the latter 4 are in the Family Hominidae.
Orangutans are in a separate family, Pongidae.
Previous phenetic (non-cladistic) classifications lumped all apes into the Pongidae based only on plesiomorphic (shared primitive) characters like hair cover and prognathism.
They are less closely related to gorillas than gorillas are to us.
The two families split at least as long ago as 15-20 million years, based on molecular data and fossil evidence.

Ah, but do they know this? Romeo and Juliet were in different families too you'll recall.