I predominantly write with a ballpoint pen, however as an affection when I write letters (which is more often than you might think) I always use quality stationary and a fountain pen. I'm very American. I know it's not commonplace, but in many ways that's exactly why I do it. There's several rather successful businesses in the US that only supply fountain pen users and collectors, probably the most well known is the Goulet Pen Company https://www.gouletpens.com/

I have several fountain pens, and vastly prefer them to anything else for note-taking (even the pen for One?Note on my Surface Pro!) My favorite was made in 1947, and still works as well today as it did then. With care, it'll still work as well when it's 100, which is a fair fraction of how long I'm expected to last (at least statistically...)

I have a friend who's into fountain pens and for a while worked for a company that sells really nice ones. In that capacity he came to know some people who collect pens.

You'd be amazed. One guy I heard of -- not-famous founder of a very famous brand -- was so into it he'd spent tens of millions building his collection, but outside the world of serious pen enthusiasts it wasn't "worth" anything near that much.

A lot of the pens one collects are very limited editions but otherwise unremarkable: say a really good pen that would cost $500 but in a different color and they only make a thousand of them in that color and it costs $10,000. (Made-up numbers but $10K is not that much in the pen-collecting world.)

I'm in the UK. They're not common, but you do occasionally see them. I have one that I mostly use because I was taught to write in the italic style [0] of cursive, so mine has an Italic squared-off nib. I don't use it every day, however.

It cost me about £40, uses cartridges, and still manages to leak (blue, washable) ink on my fingers.

[0] https://en.wikipedia.org/wiki/Italic_script