Yikes. I see Isilon and I think someone just spent 500k where they could have spent 75k and used MogileFS or similar. I suppose 37 signal's profit margins are good enough that it doesn't matter, but I'm glad it's not my money. Moving to their own servers makes sense though. No doubt that's going to save them over paying a huge premiuim for Rackspace. With three full-time people it's a good move.
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.