I have just tried my first night dive with my 4040/PT10/DX90 - being my first night dive I was completely unprepared so I taped my back up torch to my strobe and set the light/strobe to aim 1 meters in fornt of the lens and then dove with intention of only taking shots at 1 meter.
I discovered quite a host of little problems which could be listed as:
1) As both hand were taken up with the camera I could not use the dive torch I had (stupdily) attached to my wrist.
I over came this by leaving the torch that was taped to the strobe on and used it as my dive light as well as aiming light.
2) I could not see any of the controls on the back of the strobe to do "bracketing" with the DX90.
3) I could see the buttons o the back of the PT10 from the faint light let off by the LCD but the screen at the top was un-seeable. Consequently I felt for program mode and left it there.(whether this had any use I am not sure)
4) All the movement of using the setup as the dive light moved the camera line out of sync with the aiming light - the PT10 with the counter weight seems prone to this slippage and consequently quite a few of the shots were out of frame.
5) Whilst my "aiming light" was great for seeing everything as a dive light - I could see very little in the LCD screen and a lot of guess work on framing ensued.
All in all I was quite impressed with some of the results - considering they were total luck - but was left with the impression that a head mounted light was a dfinite need if I try it again in the future - just to see what I am doing.