Sometimes I get a few per day. I only know that because my Linux kernel configuration happens to have whatever settings enabled to get them reported in dmesg.

Systems with "consumer amounts of RAM" are often run with what you might call "consumer amounts of sysadmin knowledge" and not notice the errors.

One time I took a working workstation from my home to my parents' home to give them. When I booted it up it gave a lot of strange kernel errors which I googled and discovered were reports of ECC correction. I reseated all DIMMs and it was fine. If that gave errors a few times a year instead of thousands of times on the first boot I wouldn't have noticed.