I have a Dell Mini 311 ION netbook (2G ram Atom N270 cpu) that I installed as a MD. Here are some observations:
The dreaded AVWizard black screen. No amount of pressing number keys could get the AVWizard to appear on the laptop screen or a HDMI connected TV. After hunting down a VGA cable I found the external VGA connector does work. Even using the AVWizard I was unable to get a picture on the laptop screen or HDMI. Ctrl-alt-f1 etc. gets me a text console on the laptop screen. The two ways I would occasionally want to use this as a MD are stand-alone with it's own screen or via HDMI..
Sound - every time you run the AVWizard and choose the "no sound" option it resets the volume to 23% and unlike other the other options it does not give you the chance to adjust volume level before continuing. A minor annoyance, but for consistency if nothing else it should bring up the volume level screen as it does for the other options. Also, the first time I setup a MD I always need to go into the KDE desktop, open the mixer, and increase the volume on other things like headphone output or whatever other non-master volume options affect output.
VDPAU - I set the video card to GeForce and hardware acceleration to vdpau but I'm not sure it's working. I tested both hulu, which plays almost perfectly in windows, and a HD channel in MythTV via HDHomeRun, which plays great in Windows using the HDHomeRun QuickTV app. Neither one are watchable. Hulu I understand, the hardware accelerated flash drivers are still in beta, and I'm not sure if they are installed in LMCE at all. It's the MythTV performance that has me concerned. I am under the impression that the current MythTV in LMCE supports vdpau and clearly ION netbooks can play full 1080p HD video using hardware acceleration. Am I missing something?
Boot time - a bit slow but not all that bad.
Overall responsiveness - I'd say pretty good. I haven't played with it much, but I didn't notice any issues. Scrolling through a long list of videos it page flips smoothly (another ION thread lists jerky scrolling as a problem).
I bought the netbook to use mainly as a netbook, as a MD occasionally. It would be nice to use it as a small stand alone MD in my office, but if I can't get it to display on it's own screen then it's not really an option. After testing it as a MD I'm having second thoughts about going with AcerRevo 1600's as MDs. Hulu has always been a "probably not" item on an ION box, but HDHomeRun/MythTV/HD channels is important.