I agree with Lanosalf. I found out the hard way that the USB ports would be powered off if you turn off the screen using the power button (I'm using an U2311H) and it did happen to me midway through a large file transfer to my external HDD. One could hardly be faulted for expecting Dell to make a better "design choice", if indeed that's what it was.
Yesterday, I bought 2 Dell UltraSharp LCD panels and today this flaw hit me. It is a very huge flaw turning USB hub off, when you turn off the monitor. I myself am IT engineer and I "design choice" is pure crap, this is really a defect.
I just found this "feature" on my U2412. I agree with all the other posters. If this was done by design it was a terrible design decision. It makes the USB hub on the monitor quite useless. I'm an experienced computer engineer and I have to say that allowing independent power control to the screen and USB hub should be quite simple.
Hmm this is wierd. After having my pre-owned U2410 for about a month now I've watched several threads about the different faults and problems that people are coming across. This one in particular had me interested because I also would say that removing power from the USB Hub when the monitor was switched off was an inherent design 'fault'.
Then today, whilst charging my mobile phone via USB on the monitor I decided to switch off the monitor power and see what happened - and my phone kept charging. So I then switched the monitor on and initiated copying the pictures folder from the phone to my Workstation - this folder is 761MB and Windows informed me there was more than 4 minutes to go to completion of the copy. Straight away I switched off the monitor and left things for 5 minutes before switching it back on. The copy had ended and the complete folder had been installed to my C: drive.
Remember, my phone was connected to the side USB port of my U2410 and the monitor was powered completely off by it's Power switch whereby the Power LED was not illuminated. So I can confirm that the (my) USB Hub remains powered even when the monitor is switched off.
I have repeated the above and have the same results - another folder successfully copied and my phone charging with the monitor switched off.
This can only lead me to the conclusion that the other posters in this thread do have faulty monitors.
Just realised none of the other posters are using the U2410.
I need to get more sleep instead of reading these bloody forums.