Say well-known human guy gets drained by a vampire. Do his friends still recognize him even after his physical changes? Or does his appearance change enough that he's no longer recognizable to those who know him? Take things further, what about a Troll that turns into a Dzoo-noo-qua? An Elf that becomes a ghoul? There are people I know who I wouldn't recognize if they shaved, so I wonder how much different these infected qualities make a chartacter look.

It would be interesting for a backstory. Guy is an urban brawl player of some fame, gets bitten by a ghoul and turns into one. how does the public treat him if they even know it's him? Would they recognize him for who he is or would he just be some other twisted ghoul?

I would say yes. Vampires don't really get that much in the way of physical changes, as far as I know.

Gouls IMO change more, though likely still recognizable.

Dzoo-noo-quas I don't know enough about.

Generally though I'd say, "Yes, you know it (is/used to be) That Guy."

Dependent on the infection, but generally yes.

Vampires, for instance, get slightly paler & somewhat elongated canines. You probably wouldn't even realize they are a vampire.

If youre a nosferatu, your going to lose ALL your hair. Good luck getting that deltaware fiber-optic hair installed!

Just get a wig.

old tech beats new tech AGAIN.

Yeah, because bald people who shave are so rare.

Vampires and banshees will easily be able to pass as human/elf after the transformation (unless you assense them or do a blood test).
People who know them well would probably wonder if they're sick or something like that, especially in the case of banshees. Due to paleness and stuff like that.

Nosferatu are a bit easier to tell, but being pale, bald and emaciated is still within the range of what can pass as human (though they will look damn creepy with that whole Max Schreck thing they've got going).

With the rest of the infected, the transformation will be obvious unless they do something to disguise themselves.
Note that in the case of wendigo and goblins, the rules state that these characters loose the Human Looking quality if they have them.
Most would still be easily recognizable as the same person, though wendigo, mutaqua and probably also dzoo noo quaa and grendels may be an exception to that.
With those, even people who knew them well would likely pause for a moment and think "wait, i know that guy" before recognizing them (given that they don't run away screaming/pull a gun and shoot them or whatever).

Then there's cases where the infection triggers dormant metagenics. The victim doesn't only wake up transformed by the infection, but also SURGEs.
How recognizable this is, or inhowfar it makes the person unrecognizable to people who knew them before, depends on the individual metagenic qualities that apply, of course.
A vampire with Nasty Vibe would really make people wonder what happened to him, but they won't go all "oh right, you're a SURGEd vampire, bring out the stakes!" (same for Glamour, but remember : if it sparkles, we should probably kill it).
If, on the other hand, the character develops metatraits that drastically change facial features, such as Greater Fangs, Cyclopean Eye, Raptor Beak and the like, there might be some trouble when he goes all "don't shoot, it's me!"

Enter most TF* fiction ever written.

*Transformation

Sure wish I had some time to answer this properly. Alas, though, I don't. One of these days, though, if it's still around, I'll give you my own take on this.

Meantime, I need some popcorn....