Earlier today I noticed  the compiled i386 showed up in R6875 (05JUL2011) and thinking about my Pentium-3S (A 32-bit CPU) and a few HD's I have lying around I thought this would be fun to play with.
I downloaded the -i386.ISO, burned it onto a CDR, booted from that and succesfully put it on a (4GB) USB-stick (As far as I can tell it wrote around 2GB to it).  Then I had some trouble getting my motherboard (not the P3 but an IP35-E) to boot from the USB-stick but that also went well in the end.
FreeNAS started to boot but dropped me to a prompt with an errormessage and then waited for manual input:
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Verifying DMI Pool Data ......    (This is the BIOS booting)
\|/-\|/-  (Turning, booting Freenas)
error 1 lba 181344
No /boot/loader
FreeBSD/x86 boot
Default: 0:fd(0,a)/boot/kernel/kernel
boot:
error 1 lba 181344
No /boot/kernel/kernel
FreeBSD/x86 boot
Default: 0:fd(0,a)/boot/kernel/kernel
boot:
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I'll try to find a way to examine the structure on the USB-stick and find a solution, or after reporting this here a future nightly build might be able to boot out of the box, or somebody else recognizes what the problem here is and can give me a hint.  I'll pick any : )
And like JStrebel wrote, thanks for including the i386 this fast.