kpf,
Unless there is something what Sparc can do that X86 cannot do. (Which I would not be able to see).
It's called "throughput computing"(it has very much in common with the more popular "virtual computing")combined with excellent reliability. IMO, That's where any x86 design will always lag SPARC, Power and IPF. To compensate this lag OEM's must scale Opteron *up*, which is bad for the reliability, or *out* which is not suitable for all workloads.
So, I tend to see that there will be high end low volume designs for quite some time.
regards,
chr