I've toyed with it, not sure if that qualifies as "used". As a DC sysadmin I live off backports and patches (CentOS). 99% of our deployed OSes are all supported a long (to very long) time.
I used to do that but having had certain duff kernels and SMB packages out of RH, they can go to hell.
This one took out our SMB/CIFS implementation in CentOS 6.2 forcing us to grab some windows licenses in the end (which I will add has been damn reliable):
Well, I won't turn this into a thread to fix that problem, but have you tried these packages?
http://enterprisesamba.com/
Having said that, switching to OpenBSD is not as simple. It's not just some random web server with 2 sites on it; we're talking many, many servers with a great range of software running on them and so on. Some of this software will not even run on OpenBSD at all and so on. The problems are many. :)
The big linux distros - buggy as they are - are here to stay.
Also, some interesting "statistics" from $dayjob. Our DC workload (dedicated servers) is mostly web stuff; when I joined the company in 2009 there were a reasonable amount of FreeBSD servers around; that number is now 0 (or very close); my opinion is that it went "extinct" because of poor binary updates and package management as well as lack of long term support. CPanel stopping to support it was probably the last nail in the coffin.
I'm seeing a similar thing with Debian, Ubuntu LTS took over that customer base.
OpenBSD - from our pov - is facing the same issues. I'd love to see more BSDs deployed, but this will not happen unless the above points are addressed. Add to that the lack of "kickstart"-like functionality, as well.
Okay, what I'm about to say might not be too popular with some people, but I'll say it anyway:
How much did you pay for CentOS? Perhaps if more people were willing to pay for RedHat and/or Samba, some of the more obscure bugs would more readily get fixed.
In the general case, developers need to put food on their dinner table and put a roof over their heads. Good quality "free" software only goes so far, OpenBSD pulls it off because they limit the scope of their efforts.
So, instead of complaining about CentOS, buy some RedHat licenses. The end result might not be any different but you'll at least have paid for the right to complain.
This one took out our SMB/CIFS implementation in CentOS 6.2 forcing us to grab some windows licenses in the end (which I will add has been damn reliable):
https://bugzilla.redhat.com/show_bug.cgi?id=476442
Still broken in CentOS 6.5 and Centos 7.0. Many people have raised this issue (google it) and it's always "fixed next release".
Patched and built my own kernel in the end but by then it was too late.
No thanks. Had enough of crap like that.