Guh-nome for the software. It's a play on how GNU is guh-noo, which is a play on the pronunciation of the animal called gnu to differentiate it. This is what happens when you let software developers name things. I would know, being a software developer.
I'm not gonna say it's wrong to call the animal a guh-noo, since there is a G there after all, but pretty much every source lists "noo" and "nyoo" as the two pronunciations.