The Spinpoint F4's are quite new, so I can't imagine there'd be many people using them. However, the F3's are quite good drives from what I've heard, and the F4's are supposed to simply improve on those. As far as I know, the only real differences are higher platter density and lower power consumption.
The other difference, and the reason I decided not to go with them for the NAS I bought this week, is that the F4EGs are Samsung's first 4K sector drives (to the best of my knowledge).
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