Sure I can’t say anything about the Universal Image thing except that it works in my enviroment and with 10.4.5 etc. pp. – I’m here because of the .plist edit “hack”.
And this is working, it’s done with a snap and I do not see any risks.
Today I created an Universal OS X (as described on Mac OS X Hints) for our Netboot Server.
Just for testing I started a 1,8 GHz PPC iMac G5 and an Intel iMac at the same time. The result was that the Intel iMac booted in the half of the time.