I've been carrying one since 2010. I bought it used when they were in low supply and high demand, and happened across it while "popping in the store for ammo or something."
Mine has yet to malfunction beyond the one time the slide closed on an empty case that had fallen back into the ejection port. Yes, I saw it happen.
The PF9 is light and hard-hitting, on both ends. It's rude in the hands, and more than a few magazines at a session will make you feel like you've been high-fiving a hammer, but it's certainly manageable for its intended mission. It does require a determined grip, and is reportedly easy to limp-wrist. Mine feels best with 115-grain ammunition, and that is what it's loaded with, but it's likely sighted more for 124-grain fodder, so it hits a little on the low side beyond 15-20 feet or so. At 25 yards, aimed head shots hit mid-chest.
The trigger is firm and not for the Glock-minded. As a well-experienced revolver shooter, it didn't occur to me that it's crappy until I read it on the Internet. It's neither a Glock trigger nor a match-grade one, but it's perfectly functional in a defensive or fighting context. Pistol snipers, look elsewhere. The trigger action is of a hybrid-DAO mechanism, with the hammer only fully at-rest if it's dropped on an empty chamber (or dud round.) Between chamberings/shots, it's partially-cocked; each trigger pull moves the hammer the rest of the way to the rear and then releases it. The reciprocating slide resets it to that partially-cocked position. There is no "second-strike" capability, but you can reset the hammer by retracting the slide about a quarter of an inch; you'll hear it click.
The Kel-Tec P11, by comparison, has a true DAO trigger/hammer mechanism, with the hammer always fully at-rest.
My blued slide started to rust about two years after I got it (my gun appears to have been made in 2006) so I upgraded to Kel-Tec's hard-chromed one. It's held up well.
With all of the other micro-nines that have arrived since the PF9 opened the market, the KT may not be quite as relevant anymore, especially since interest is shifting toward micro-double-stack nines these days. Still, the PF9 remains the lightest and flattest 9mm pistol on the market with a seven-round magazine (The Diamondback DB9 is smaller, but gives up a round in capacity.) I keep wanting to switch to newer guns, or even older revolvers for carry, as I do appreciate steel, but I keep coming back to the KT because it just makes sense, though I do have a Taurus G2C I have yet to try. Still, for concealability, there is no comparison.
Incidentally, the year after I got it, I bought a new P32 for deep-conceal. It has backed up the PF9 pretty much every day since.
Hope this helps a little..