After the Cylon ambush, when the government asks Balter to build a Cylon detector, they have just recently learned there are "skin jobs" (as they call them) that look like humans, but they aren't sure how to find them.
Later, they know Sharon Valerii is a Cylon, but there's no indication they have examined her to tell how they can detect a Cylon. And, of course, Sharon Agathon, a humaniform Cylon, and Karl Agathon, a human, have a child, Hera, together. The second fact says that Cylons not only have genes, but that their genes are compatible with human genes.
Humaniform Cylons have blood, they have genes that have to be quite close to humans. They cry, they sweat, and the only three indications we've seen that they are different is when Leoben breaks down and is not able to function due to radiation at Anchorage Station and that they do, somehow, download to the nearest Resurrection Ship (if one is available) when they die. (As best I remember, it's never revealed how the Cylon detector works, but since Baltar needed a nuke to build it, it's possible it was based on observing reactions to radiation exposure.)
There's no indication they find wiring or other mechanical parts in them, but the other difference from humans seems to be that they can interface with the right wiring that connects to Cylon machinery.
Which leads to my question: Just how human are humaniform Cylons? They can't be too different (if there were wiring, it'd show up on x-rays, for example) and it would seem the main thing tying them to "the enemy" would be their memories and identity. Their bodies seem to be almost completely biological and not at all mechanical.
So how human are they? How do their bodies differ from humans?