I used Migration assistant from my old PB G4 (Tiger OS) to my new MBP (Leopard) and had 1,000,000 problems. It came down to old software messing up finder causing many many problems such as freezing HD.
I zeroed my hard-drive, re-installed OS Leopard and installed all apps manually, collected music and photo files manually, and set up mail, bookmarks, address book manually.
Now my mac is back running intact, faster than fast with no problem to last. 🙂