I posted this on Speedlights forum but there is so little activity on that forum it seems pointless. Anyway I understand the SB 400 does not work on the new D7000. I use it probably about 20% of the time (SB900 is my main unit) & I intend replacing my D90 with the D7000. Annoying that all my lenses will fit but a little flash won't. I don't remember where I read that it is not compatible.
The only incompatibility is lack of CLS functions that is one of the main reasons to get Nikon flash systems in the first place. So the 400 will work with the D7000 the same way with the same features as it did with the D90. I've never been a fan of the SB400, it really is no more powerful than the built-in flash and only has the one axis tilt of the head as the advantage over the built-in. A pocket mirror held in front of the flash head to redirect the built-in light is more flexible in bounce. A SB600 is a lot more useful than the SB400 and not as big as the wonderful SB900.