You can also skip few steps in that guide. You don't need to rename bootinfo.txt or bless it (if you don't touch it). Unless bootinfo.txt has changed of course, but it usually (never?) does. It's enough just to replace boot.img and that's it.
This method has worked for me too, but it's not officially recommended to update the live system, because in theory it can cause some unexpected errors. I'd recommend to do it after fresh reboot at least.
Other safe discless method is to boot the ISO from USB memory. It's practically the same as CD boot and it's recommended way too. You can find official guide for it.
+1 for USB or CD boot - the simple (and fail-safe) methods, no messing with the boot partition.
It's easy enough to put together a yaboot-based boot menu that offers all the options (boot from HDD, boot OSX, boot linux, boot from USB, boot from ISO, etc), but any boot menu adds a few seconds to the boot time.
For everyday usage, unless you regularly boot into multiple OSes/versions it's more annoyance than use. (The one blessing is that once configured, you never have to bother with OFW for anything ever again.
)
