Actually there are several games that already do. Such as Company of Heroes, Lego Star Wars 2, among others. So there are about 5 games right now that use DX10. Just that there is only 2 types of DX10 cards out there right now.
The nVidia 8800 line and the ATi R600 line. Other than that there isnt a DX10 card out.
Still there is no major reason to wait. A service pack is just the updates to date and maybe a added feature like XP SP2 security center. Other than that it is just the combo of all updates.