I'd thought that if you wanted to boot Intel Macs you needed to use the recently available GUID partition table, mainly because that's what it says in Disk Utility when you format the drive. In fact, as it turns out (at least as of Mac OS X 10.5.5), using the Apple Partition Map (APM) boots Intel Macs perfectly well. It's exceedingly useful to have a partition format that will boot both architectures, particularly at the museum, where Intel and PPC Macs still very much coexist.
In fact, my Mac is a G5, but all the new hardware is, of course, Intel-based. And I'm trying to create a master build image for setting up new machines. Generally the way I do this is by making a test build on a firewire partition. I can boot into this build and tweak it until it's perfect. And when it is, I image it to an ASR disk image for NetBooting. I was worried that architecture limitations would make this painful — that booting into my test build partition would be impossible on my PPC Mac because of these restrictions. Glad to know I can just use the old reliable APM for everything and it'll do what I need.
Not sure when or how they worked this out, or why the language in Disk Utility has gone unchanged. That fact does give me pause. But so far booting Intel Macs from APM partitions has worked perfectly for me on multiple machines.
UPDATE:
More info at Apple's Secrets of the GPT Tech Note, via Jeff in the comments.