my experience (and my experience in this is a few years old, so take that for what it is) has been that commercial SAN/NAS products have a significant reliability or performance edge over their open-source competitors. Note, I said reliability /or/ performance; the key bit you get from netapp or emc that I can't do with a linux box is cache coherency across multiple heads.

If you fire the money cannon at NetApp, they'll give you two heads, each with write-back cache in it. when you make a write, it will write to each head before returning, so either head can crash or lose power at any time without interrupting anything, and you get the speed of write-back cache, which is pretty great.

Now, the problem is that NetApp and friends charge a /ridiculous/ premium for this. I'm not saying it's a good deal. I'm just saying that /right now/ as far as I can tell, there are things you get from paying netapp and the like that you can't get from freenas.

Personally, I'm cheap, so I use local storage, and end up paying a whole lot less for disk. But if I was successful at selling a product that was not tied to my costs? then maybe my decision would be different.