There are many factors which should be taken into consideration. How long do you wish to keep data on disk? How much data do you back up each week, etc. I've been using the SATABeast for about a year now and they scream right along. I have 1 in my main data center which serves as a primary backup target. I also have 3 in my remote data center which serve as targets for auxiliary copies from the first system. I then spin 3 tape copies from the second set of SATABeasts. I keep data available on disk and tape for 28 days onsite. I'd say any SATA / SATA-II array will significantly boost your backup performace and it will without question boost your restore times depending on whether or not you retain the data on disk. Take a look at the SATABeast - I've been really happy with them. I was using STK SATA arrays before I got the SATABeast. STK's were faster than tape, but the SATABeast is almost twice as fast in my environment.
Hope this helps.
