I played with a D-Link DSM-520 a little bit before I returned it.
It did audio, video, and photos well, and could also play the Smartlists (I tried smartlists for Audio, but not for Photos).
However almost all of the current UPNP devices in the market have problems with showing photos properly. They will either get the aspect ratio wrong (i.e., force stretch a 4x3 picture on a 16x9 HDTV screen), or do a horrible job of downsizing to fit on the screen (i.e., taking a 5 megapixel picture and showing it on a 1280x720 screen), or are too slow for most purposes (may take more than 5 secs to load the next picture).
The only Upnp device that ever got "photos" correctly, was the "Roku Photobridge" (here is a review of it from
PC Magazine) but Roku Labs has discontinued that product.
The good news is that the new generation of Upnp devices are supposed to solve most of these shortcomings, for example
NetGear EVA8000 and
D-Link DSM750. These products were all announced at CES2007 a couple weeks ago, and are not yet on the market, but should be within 2-4 months (thus why I returned the DSM-520).