If you are going to choose a NAS, keep in mind many out there have the same DLNA functions, so evaluate a few brands.

My NAS of choice is still a ReadyNAS. But knowing that some of the key (pre netgear) engineering talent has left recently has me shaky about the future. Waiting to see the impact, if any of their departure.

Almost any NAS will do pure DLNA sharing (ie, it send the file over the network to a playback device, and all decoding happens on the receiving end) just fine. You will run into some issues though if you also want to add video transcoding (ie crunching a big HD file down realtime to play on an iPhone) with most units. Most NAS devices these days are using Intel Atom processors, which do fine for NAS and basic DLNA serving needs. Some NASes offer more normal desktop class processors, so transcoding becomes a possibility.

Fan noise on the ReadyNAS side varies. The 4 bay units are noticeable if you have them in the same room, but may not be annoying depending on your tolerance. My older (and no longer sold) NV+ was the loudest, my Ultra 4 (same form factor, newer guts) runs quieter, but still not desk quiet for me. The two bay units you will notice hard drive noise more then you will the fans.