Hi,
I've had a DSM-750 now for about 2 years and I've been very happy with it. I primarily use it as a music server as I have a subscription service to Napster and the DSM supports Digital Rights Management so I can listen to all my downloaded songs on my stereo. This setup works great. I also use the DSM for viewing photos on my TV as well as movies I've taken with my digital camera. I generally have not used the DSM for watching downloaded movies although the kids do this using the USB direct connection and that seems to work reasonably well. I primarily use my home computer as a file storage system but I also have a network drive and the DSM connects to it without any problems.
I've always used the DSM in it's default mode (Media Lounge?). Are there any particular advantages to using the extender mode? If I set up for extender mode can I revert back later?