I dragged this up from the depths because I just purchased a 2011 Mustang with SYNC and I'm happy to report it works pretty darn good with the n900.
I did have to load my phone book with the usb app. Other than that the voice controlled dialing works great as does the bluetooth media. I have yet to try the texting feature as I don't text.
I plugged in a USB stick with over 2000 songs and it's a real treat to be able to select a track verbally! (you do have to remember the name, but that's my problem)

All the SYNC features seem to load and connect almost instantly, which is way better than my past usb and bluetooth experiences. I think Ford and Microsoft did a good job on this project and I never thought I'd say that!