I’m using 10-bit only with FCP 5 and Tiger. You need a capture card that will support 10-bit (Like AJA’s Io, Kona2, or Decklink’s cards) to capture, but you can also import 10-bit uncompressed footage and work with it provided your drives are fast enough, and you have the appropriate 10-bit codec loaded. AJA has a free download called AJA KONA system test that will tell you how much data your drives are capable of writing per second and how many streams you can get in various resolutions.
I believe Motion 2 also supports 10-bit, because Apple’s video apps are resolution independent, from DV to HD 1080i. I have opened my 10-bit SD footage within motion with no problems.
-mjd