A few things that might of use:

1) Installing Hardy as the second OS (no Windows) was a bit of a pain. I was trying to follow instructions that recommended that GRUB get installed on the partition that Linux was installed on. Turns out that in the case of a dual-boot (where we don't have to care about Windows) you can just install GRUB where it wants to be - in this case (hd,0). OS X doesn't care, and Linux is happy. Haven't tried this with a triple-boot yet, though.

2) browsing the rEFIt site I found this:
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If you want good graphics support in Linux, you must boot it using BIOS compatibility mode. This also means using LILO or GRUB, and having a MBR partition table (either hybrid GPT/MBR or plain MBR).

The X.org / XFree86 drivers for Intel and ATI hardware require a Video BIOS to initialize the card. The Linux text console also relies on the Video BIOS. Apple’s firmware only provides a Video BIOS when booting in BIOS compatibility mode. Without it, you only get unaccellerated frame buffer graphics.
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So I guess that's why wobbly windows works in Linux now.

Long story short: use an MBR when setting up dual/triple-boot Macs.

3) Did a quick test with rsync-as-machine-update-mechanism: I created a wee disk image pair, then updated the source dmg, re-ran rsync and found that the entire dmg was "uploaded". It doesn't look like it's diffing the binary files and merely uploading the different bits. This is strange because I was quite certain that *was* the way that rsync worked. I'll continue looking in to this.