well if u do decide not to.
it is easy later on to buy a USB3 add on card if you need it in the future.
Possibly. Regular PCI slots don't have a fast enough data transfer rate to support it. USB 3.0 could even technically saturate a PCIe x1 slot. So I'm betting most of the true USB 3.0 cards are going to be PCIe x4, and how many new motherboards have that? Which means you'll most likely have to sacrifice a PCIe x16 slot to get a couple of USB 3.0 ports -- and no one wants to do that -- or try to find a PCIe x1 version and possibly settle for somewhat capped performance.
On top of which, the cards themselves are going to cost money, and it's, like ... $20 or $30 right now to get built-in USB 3.0 if I recall correctly. So I'd just get it now if I had the choice.