The sticky, stringy stuff isn't spit, it's mucus from the throat. That's why it sticks to the mouth AND the penis: it's thick viscous.
And yeah, the chicks with long nails freak me out.
I also wonder how hard it is to mask the pain some women have to be feeling when a dude's huge dick is banging up against her cervix.
Or how they handle a dick to the ass with just spit for lube (which is really not thick enough for comfortable anal, I'm sorry) and/or don't have any visible tearing. I'd say they use a butt plug and remove it before the scene, but a lot of times they show you the woman's ass, and you can see it hasn't been...erm...dilated, for lack of a better term.
As for the awkwardness, I think we've all seen scenes where the actors were really mechanical and had no chemistry. I often hear porn stars complaining about newbies and how they don't understand how the process works, so I'd assume a porn star knows all about angling themselves to the camera and such. BTS clips also often show the pornstars being walked through the basics of the scene, so it's often planned out beforehand rather than spontaneous.
