My GA-MA78GM-S2H with LawlessPPC 10.5.4 boots about under 20 seconds (14 to be more precise - stopped that with my watch).

Maybe it's the fast CL4 memory or else, I dunno. I also erased the Extensions.mkext (the first thing I always do with a new Rig) and cleaned the final setup thoroughly with Onyx. Before I did that boot time for the OS was about 2 minutes.

Of course, boot time is from where the OS begins to load - with turning the machine on with a cold start it's total time is roughly 40 seconds (darn ACPI load time).