well, I have downloaded and installed Solaris 8 for Intel and I ran it for a while. The install was easy enough and it ran great. The reason it doesn't run as well on an Intel chip is because of the multitasking capabilities that the SPARC has over any intel chip. Intel's will bog down if you get multiple things running at one time, whereas a sparc would still run strong.
I guess thats why solaris is free on Intel's up to 8 processors.
good luck