12.0-RELEASE: I2C errors, fan speed problems, and USB problems

[Koakuma]

So recently I booted the 12.0 memstick image on my G5 (11,2 dual-core,
2 GHz, 16 GiB of memory), in the "Live CD" mode to try things out.

For some reason, the OS runs very slowly and it gives me those errors
all the time:

max66900: iicbus read failed
max66901: iicbus read failed
iichb0: I2C error
ds16310: iicbus read failed
ds16310: ds1631 read config failed: ffffffff
ds16310: iicbus read failed
ds16310: ds1631 read TEMP failed: ffffffff
ds17750: iicbus read failed

And the fan keeps running at max speed.

Also, there's another weird issue:
If I disable SMP, all USB peripherals (except the included Apple A1048
keyboard and the flash drive I'm using to boot) won't work at all.
On the other hand, if I enable SMP, all USB peripherals will work fine,
but I get the random hangs, similar to the ones reported by other
G5 users.

Any workarounds for those issues?