I got Leopard on day of install and after "amending" the installer to make a 400MHz G4 the minimum Spec I installed with out problems.

I did an Upgrade install over OS X 4.10 Tiger and have had zero problems. Not one, which was strange as I was expecting loads of them.

All works well, system feels somewhat faster under Leopard than Tiger and after a week I deleted Tiger from my IDE drive (I had backed it up on there just in case I needed to go back to Tiger).

I find that Time-Machine works well using the USB2 drive as a back up.

The Lacie D2 has been "Clicking" and failing to boot up unless I remove power & fw cable a fw times but that appears to be quite common.

Overall a good upgrade

System is a Dual 533 G4, Nvidia GeForce6200 GFX, Sonnet Serial ATA with 2 drives in a striped array which I am booting from and 80GB IDE Drive for data, Lacie D2 FW drive and a USB 2 Drive, PCI USB 2 adapter fitted.