I have ADHD, I'm prescribed Concerta (which is a delay-released form of Ritalin). Because it's a gradual release, that probably affects my experiences.
But generally, the noticeable effects for me are very subtle, I've joked before that if someone swapped out my drugs with a placebo, I wouldn't be able to immediately tell. It doesn't help me at all with my time blindness, it doesn't improve my memory (that I can tell). And (contrary to other people's experiences) it doesn't even really help me avoid getting distracted (for example, I'm on HN right now). But what it does help me with is starting tasks and getting over executive dysfunction.
With my experiences with ADHD, there's this huge gulf between wanting to do something and actually doing it. So what I notice when I'm on Concerta is that it lessens that gulf. So if I tell myself to go put clothes in the dryer, then I actually go put clothes in the dryer, it's not as much of a monumental multi-step effort of "stand up, put on your shoes, find the laundry room key, walk out the door."
This could be related to the time-release, it could be that people taking this in non-prescribed settings are taking much higher dosages, it could be an individual thing? But I'm always a little weirded out by the idea of people getting addicted to this stuff, because I have to set timers and actively remind myself to take it. It doesn't make me feel wired or unable to sleep or constantly focused. When I started taking Concerta, I spent multiple months with my psychiatrist just tracking day-to-day tasks like how often I ate, whether or not I was brushing my teeth -- because without the charts I didn't feel confident that it wasn't just a placebo effect, I needed to track data to know for sure that anything was even happening.
I'm assuming that people using unprescribed Ritalin are taking it in different ways and in higher dosages. But... I mean, it's not going to make you smarter, at most it seems like it's going to make you more focused on something? But speaking as someone who is constantly hyperfocusing and hyperfixating on things, there are a nontrivial number of college/life tasks where hyperfixation is not helpful and where it would be convenient to be able to turn that behavior off. I spend a lot of time trying to manage hyperfixations, they can be beneficial but they're not universally good.
But I do know that Ritalin/Adderall affects different people differently. Back when I was in college I was not aware of people doing stuff like this as a norm, but I don't know how I would have known about it, so maybe it was happening in other circles.