Outside of OpenFiler, your options would be other NAS OSes (FreeNAS, NASLite...), dedicated NAS appliances running custom software or completely rolling your own with a mainstream linux distribution (or Windows if you really want).
I have been experimenting with FreeNAS and OpenFiler for the past month or so. I am putting my eggs in the OpenFiler basket. I haven't been running in a production environment, but all the research I have done points to OpenFiler as being the Enterprise solution compared to other NAS OSes and NAS Appliances. In pretty much all performance reviews I have seen it out performs those solutions. This is of course based on the hardware you are running from and how you tune the server. Also, based on my research, anyone who has purchased the support package has mentioned their support is very exceptional.
You can also see someones comparison of FreeNAS to OpenFiler here to get some ideas of what sort of performance they saw with OpenFiler.
I have not compared OpenFiler to custom solutions though. Some people prefer to support and maintain a more common linux distribution like ubuntu and expose NAS features manually. I think this would be the preferred solution if you are running on uncommon hardware. That is something that I am not interested in doing. I'd imagine you could get as good or possibly better performance with a custom solution depending on your hardware and the support for it.
So as long as you have got a decent hardware setup and a support package, I'd say OpenFiler would be a success in production. Just be sure to check the hardware compatibility page.
Additional Edit: Make sure when you set up openfiler you do it with all new drives which do not have any data. Openfiler uses LVM and doesn't play nicely with drives with existing partitions on them. It will probably be easiest to setup openfiler with nothing on it, then migrate your documents and images later.