I should clarify, as I was in one case totally wrong, and in another partly.
White balance settings do work, including preset white balance, in video modes.
They day I received my d300s I did a quick test to determine whether or not the information on p. 58 was correct, and I didn't notice the f/16 note. I set the f-stop to f22, pressed dof preview, noted the size of the physical aperture, then pressed live view, and noted that it was bigger, so I assumed incorrectly that the information in the manual was wrong. Lesson learned.
Mostly automatic would be more appropriate term.
Glad that you confirmed that it is possible to manually set aperture in video mode. Not sure why you did such a complicated test though. A simpler and very straight forward test would be (perhaps others would like to test) to in Aperture mode (before you press LiveView) select the largest aperture. Then go into LiveMode and press record. Notice the short depth of field. Then exit LiveView mode and select the smallest aperture, go to LiveView mode and start recording. Now you will easily see the large depth of field.
Being able to manually setting the aperture to control the depth of field is very useful when recording video. Both on land and under water.
Being able to manually set the white balance is really good, especially when you are recording underwater in natural/ambient light (i.e. no light sources other than the sun).
This in combination with exposure compensation and exposure lock makes it possible to get in control of the video recording.
Don't forget that you can also control things like contrast, colors etc by altering the color setting modes in the camera (the same settings that are used for jpg-recording).
FPS is fix to 24 fps, so if you are OK with that, that's fine.
Being able to use the autofocus while recording is nice.
So, even though you can't control ISO and speed, I'd call it mostly manual ;-).
Don't get me wrong, I would have very much appreciated the control of speed and ISO, but I think we should concentrate on what we really can control and how to optimize the controls with the D90 and D300s. People with Canon D-SLRs seems to do tons of uw-video and upload really nice looking uw-videos all over the net. The D90 uw-video above is the first one I've seen! Don't forget that the D90 was released before any Canon D-SLRs could do video.
Recording video is not super easy even with an expensive Canon 5D Mark II. They have many of the "problems" that we with D90 and D300s have. But, they have found ways to overcome the problems. Special settings (go for a large DOF), special lenses (rectinal wide angles), special video techniques (sloooow movements etc), setting the focus prior to recording, planning your video shot, manually white balancing every 5th meter etc etc etc. Most of those tricks are possible for D90 and D300s owers too.
This thread started out as a "how to" record video on the D90 and I have no intention of changing it into an "who's wrong and who's right" thread. So, please people keep posting your tips and trix on how to optimize our uw-videos with D90 and D300s D-SLRs. I started with a bounch above, please add as many as all of you can think of and finally please post some more uw-videos taken with a D90 and D300s (I will hopefully make my first try next week in the dark waters of the Swedish west coast). Why not try both macro and wide angle. I'm sure it's possible.
Finally, as with all uw-photography "if it was easy, it wouldn't be any fun". ;-)