Are you sure about that M'texas? According to their website having four 1TB drives gives you 2.7TB of storage with .9TB for redundancy, not 3.2TB of storage, and there's no way you could lose 3/4 of your drives at once and reconstruct it with a single dive.
If you are not in a big hurry the next edition of OSX will have data redundancy built in so it will manage all of this for you at a fraction of the price of the Dobro. You can buy four 1TB drives for around $400 and the 4TB Dobro is over $1,000. I would buy another 1TB drive and copy your existing and then wait for Snow Leopard to come out later this year.
If you are not in a big hurry the next edition of OSX will have data redundancy built in so it will manage all of this for you at a fraction of the price of the Dobro. You can buy four 1TB drives for around $400 and the 4TB Dobro is over $1,000. I would buy another 1TB drive and copy your existing and then wait for Snow Leopard to come out later this year.