There’s a friendly cat in my neighborhood who follows me around when I go past his house and pet him. When I start petting, he starts drooling like a faucet. Is this a sign of happiness or pleasure? Do a lot of cats do this? Or is this cat just prone to drooling?
We’ve had two cats (including one of our current pair) who drooled when they were happy, particularly when being pet.
I have seen a relaxed cat stick the tip of his tongue out, but no drooling. Have you ruled out possible abnormalities like a tooth abscess (is there obvious foul breath?) Catnip and other OD can also cause drooling.
ETA or maybe that cat is just prone to drooling, but there could be other causes
One of my two cats drools when she is happy: being brushed, being petted, etc. It’s kind of a pain because she’s beautiful and fuzzy (see below), but having her on my lap means I risk being flooded with cat spit.
I’ve had other cats in the past that also drooled when they were happy.
I’d say some do this. One of my cats is a happy drooler, the other is not. In my anecdotal experience I’d say it is not quite the norm, but it also isn’t uncommon.
Likewise here. I’ve owned four cats: two happy droolers, two non-droolers.
Come to think of it, I have seen a cat knead and aggressively suckle a blanket or T-shirt and really slobber all over it.
My sainted cat drooled profusely when happy and when stressed. On trips to the vet, he would get sopping wet by the time we arrived, and I always had to explain to the vet that it was not vomit.
I’ve got one of these. Not drooling in general, but has his favorite light blanket which must be washed frequently because at nighttime he’s all about kneading and suckling it. Only that particular blanket’s texture will set him off. Of course, petting (when he’s in the mood of course) or being brushed with a whisk broom (anytime) will turn him into a noodle that falls off of things, but that’s drooping, not drooling. 
Wife seems to understand cats well, and she says the drooling is “baby kitty” response, e.g. they drool when preparing to feed. Cats do a lot of “baby” things to get humans to care for them, including meows, drooling, etc.
One of our cats was “hand raised” as a feral kitten and really enjoys being petted while she eats. She leads me to her dish and purrs loudly when I pet her. We figure she was petted and praised as a kitten this way, before we ever met her. But she seeks this affirmation very often. As for drooling, she’ll suck on a particular blanket and knead on it when she’s in the mood.
The other cat drools when he’s feeling particularly lovey toward daddy or mommy, and will give us wet kisses. I’ve even had a cat (a decade ago) that gave us love bites when being petted / purring.
ETA: Kneading is also a baby kitty behavior, to get the kitty mommy’s milk to flow.
The same here, some cats have drooled, some don’t.
Another “some drool; some don’t” Our friends had a cat that really liked my wife (before she was my wife), and used to lie on her clothes when she left a jacket on a bed or something. And drooled on them.
Yeah, Mr. Kitty will sit with me on the seawall for as long as I want and if I’m petting him, there will be almost a puddle on the concrete from all the drooling. It can be gross if he wants to be scratched under the chin.
One of mine is a drooler and he has lost most of his lower teeth in an RTI. This means that his drooling is really out of control as he has no teeth to keep it in. I have to use spit cloths when I want to pet him 