Yep -- same thing, here. Machine is fine, but once the Sonnet-driven SATA volumes are mounted it doesn't take more than a few minutes to hang all writes; Finder freezes completely, so all related activity gets stuck. For example, I had to download the Aperture update four times (@ 20 minutes each) because the Finder froze before the software could be installed. Glad I imaged my drives before upgrading, but this is a real drag.
Speaking of drag, does anyone else have a weird window update problem, where you quickly drag something across and the screen and it doesn't move, so you put the mouse pointer back to where the window remains but when you click and hold the window appears where it should have been after the first drag but the cursor -- even when it's on the other side of the screen, where the window just was -- still controls the window? Likely other people who're seeing this have articulated it better. It's disconcerting to move a mouse over empty space and have it control a window on the other side of the screen.
Ah, and now Final Cut Pro Studio 2 won't install, having previously crashed mid-install due to the Sonnet driver problem. I guess I'll be holding off my new hardware purchases until the problems with Leopard get ironed out.