Given the difficulty Intel has seen getting the new E5 and E7 chips out I personally don't see any of the others as competition when it comes to producing a power efficient X86-64 chip for the DC at scale.
I think the greater danger isn't other X86-64 chip manufacturers though. The only real competition is AMD/ATi + GlobalFoundry and their chipset process is a generation or two behind. The greater danger is the market moving to an entirely new architecture. Think about ARM in the datacenter. Less power consumption, smaller boxes, less cooling requirements. DCs could make a strong argument it's cost efficient for them to jump and if a major one jumps, developers will probably follow. Most of what we build today uses a software stack built on top of a managed language (Java/Python/Ruby) and doesn't rely on being native compiled. It reduces the opportunity cost of switching.