I had troubles with both SoftwareSuspend2 and ACPI Sleep with the 2.6.10-rc2 and -rc3 kernels. Thanks to investigation by Bernard Blackham I’ve found the cuplrit: apparently Alsa Driver Power Management was broken in these versions.

He also provided a patch from the bitkeeper tree that fixes these issues, and both SoftwareSuspend2 and ACPI sleep work again. I’m happy. ;-)