Careful with that OEM, Eugene.
OEM hardware ususlly comes with less of a warranty or no warranty. Would you want that 5 year warranty on the Raptor or Barracuda drive? Damn straight you would. Pay the extra on hard drives and CPU's definitely.
As mentioned, depending on the product an OEM piece of harware may not come with the bundled software, accessories or packaging that a retail version would. Up to you if that is significant.
OEM software is usually sold bundled with hardware.
If you have an OEM Windows on your PC with the sticker on the side, it is locked in to that PC and you can't use it on a different one even if that PC dies. That's the tradeoff for the lower cost.
However... Every software pirate in the world claims that their burned CDs are "OEM" and that's why they are 90% off of the retail price. Those are just flat-out lies. So you have to look twice when you see ANY adverised goods that say "OEM". They will be either reduced-warranty, not legal for resale or outright phony.