Hype-threading stopped working for me (probably due to
me not enabling ACPI). dmesg output and .config attached.
-rc5 worked fine. The board is an Asus P4P800-Deluxe.

dmesg: WARNING: 1 siblings found for CPU0, should be 2


$ cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 15
model		: 2
model name	: Intel(R) Pentium(R) 4 CPU 2.60GHz
stepping	: 9
cpu MHz		: 2606.438
cache size	: 512 KB
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 2
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips	: 5144.57


Johannes