I replied to a similar question elsewhere, and wanted to offer the same advice here. According to RoadtoVR.com, who play tested the "Crescent Bay" (Oculus 3.0) build of the Oculus Rift:
“Though Oculus isn’t sharing specs for now, my best guess is that we’re looking at a resolution of 1440p or possibly higher…I would guess they are running at 90Hz right now, but I can’t be certain.” - RoadtoVR.com.
So be advised: though the Oculus website states "1080p", we're likely looking at a consumer product that can support 1440p or higher, with screens capable of 90Hz refresh rates.
1440p eliminates (or nearly) the "Screen Door" effect caused by the lower resolution DK2 and especially DK1, and 90Hz appears to be the necessary refresh rate for high speed in-game movement (either of your head, or of elements you are watching fly past you at high speed). Refresh rate is actually extremely important, as slower speeds can cause 'tearing' effects on high-speed action.
I'm assuming that mid-range builds will do alright with the Oculus, but those seeking a high-degree of immersion may at least need to invest in a powerful GPU.