I think there are some major bugs with OS X 10.5- mostly with external USB/firewire devices. I have been unable to keep a USB or Firewire drive online to copy files- I keep getting either an 'unexpected disconnect' or a 'insufficient privileges' and the transfer is dropped.
This happens to drive connected directly to the Mac Mini or through the integrated hub in my Acommdata 250GB drive. Odd part is the Acommdata drive is rock-solid- but drives connected to the 2nd Firewire port drop...
I am also seeing spotty reliability with my USB DVD-RW and Logitech Fusion camera (USB).
I am sure these will be revolved in time- but I don't want to wait with a 'broken' OS until they are fixed!
I would go 'back' to OS X 10.4 but I purchased my Mac Mini as an open box buy and there was no media (or Apple remote) included in the box; I am looking for an ISO of 10.4 on UseNET, but most seem to be hacked copies intended to run on any other x86 hardware (mostly MacDotNub and uPhuck builds)
On the other hand- Mac OS is very good at taking video from a Mini DVD-RW, importing it in to iMove and then allowing me to publish it directly to YouTube! I don't think there is anything even vaguely resembling this on the PC side.