The only precaution I would take using that method is to place all the motherboard and video card power connections on PSU1 and all the HDD and CDrom units and any 'direct' powered devices that directly plug into a PSU line, in example such as extra case fans, on PSU2.
This is exactly how my computer is set up. The Silverstone 600 powers both 7950 GX2s and the motherboard and the 450 runs everything else.
If I plug my video card and MB in one power supply