I am using Leopard on a 2.2 intel Macbook Pro. The work around seem to work and it works well tethered. There should be an update to Capture One 3.8 any day now. If you are doing a custom configuration, go for the 7200 rpm drive, the drive seems to be the achilles heal performance wise. I wish I had gotten it. I probably should have waited to upgrade to 10.5 but it seems to be working ok.
Make sure you read the Knowledge base articles. Aside from the manual install, if you want to import from a CF card, you have to drag them in manually in the finder, C1 will corrupt them under Leopard if you do the auto import.
Also works well tethered with Phase backs but not with Canon yet.
If you order one, by the time you get it, Capture one may be updated. Hopefully soon. They say they have a "team" on it.
Photoshop works great.