It seems like just yesterday we heard from David Thomas that his Samsung Syncmaster 910 MP display wasn't working with his shiny new 2009 Mac mini. Oh, wait, it was yesterday -- and David's not alone, judging by the traffic on Apple's support boards. VGA display owners who are using a Mini DisplayPort-VGA adapter should be aware that older displays seem to be having some trouble with the newfangled setup; in fact, Apple's troubleshooting steps for lack of video on the mini suggest replacing your display if it's not lighting up with the mini, even though it may still work with other machines. If your existing display is a Samsung or is more than four years old, you may want to cross-check with Apple before trying to use it with a new mini.
There's some light at the end of the tunnel, however. While it hasn't appeared on Apple's download page for the mini yet, reader Nikolay sent in word that the Mini DisplayPort to VGA Firmware Update is showing up for him in Software Update on his MacBook Pro. Since one of the listed fixes is "no video on some external displays," if you've got the VGA adapter in use and are having video troubles you may want to borrow a monitor long enough to run the update and see if that clears the issue for you.
Thanks David & Nikolay