Intels next generation of processers/motherboards come out in January.
PCIe3.0 is not confirmed to be coming out until at least Q2 2011, and that's only if we assume AMDs next processer will support it, which is pure speculation. Intels Ivy bridge processers in Q3 2011 will support PCIe3.0 though.
At the moment - PCIe2.0 8x is still used in crossfire/SLI setups. This is half the bandwidth PCIe2.0 can deliver. By the time the average gamer would actually see substantial benefits from PCIe3.0 bandwidth, their computer would be obsolete. Don't need to worry about this.
SF-2000 Sata3 SSDs on the performance front, Intel 25nm Sata2 SSDs on the value front.
Nothing else I can think of. I think buying a computer now is fine, although certain laptop users will see significant benefits by waiting for sandy bridge.