Hi,
I have 2*WD HD Live TVs, 1* original WD TV and and 1* AC Ryan HD Mini (don't tell the wife).
I am putting a media player in each bedroom, the living room and the kitchen (less boredom washing up with music or a tv show). Nope, no plans for the bathrooms yet

.
The original WD TV is not network compatible. It is hard disk only and cannot handle HD content. Fine for music and non HD T.V. shows from a USB HDD.
The WD HD Live TV works with some 3rd party USD wireless dongles (I have had a dual band Linksys dongle connected) but I find the connection can be slow so if you turn it on and then straight away go for browsing content on a NAS or the like I generally get a 'not connected' error. Using a wired connection gives no issues. It has played most stuff I have thrown at it although it can stutter with high bitrate movie rips (12+GB mkvs). It may be my encoding, maybe not. There is a pause for a few seconds which is very irritating when I first start browsing like it is cataloging content but even if browsing the USB HDD during the pause, the HDD light does not flash. This pause only happens when first turned on but it does it every time it is turned on. The interface is basic but usable (I understand there are a few improvements for the WD Hub). There have been a few firmware updates since I last used the wireless dongle so there may be improvements there I am unaware of. When you turn it off it has no lights so is good for a bedroom.
The A.C.Ryan (there is a big thread here about it) has a much nicer interface that can be 'skinned'/changed to show play sheets for the separate movies. Navigation is fairly easy and I can get to browsing my NAS server via my wired network before it even recognises a USB drive is also connected. The unit looks pretty nice with red or blue status light bar on the shiny black front. It is a little bigger than the WD. This plays the majority of content I have thrown its way but seems to stutter a bit more than the WD with the same material. I have not tried it with any wireless dongles apart from the Linksys one I use for my WD box which was not recognised. One big plus with this unit is that you can telnet to it and install / change the setup at a Linux level. There are of course limitations but you can hook into the Init process and run your own scripts. I am not sure if anyone has done so yet but it should not be too hard to build a funplug like setup as seen on the DLink DNS-323 turning the unit in to a small, all be it low powered, Linux server. The program that plays the movies (magicCD or something like that IIRC) is propietry though so, last I read, you cannot modify it without issues. High bitrate large files are likely to cause issues with this player though as the CPU for the unit also handles the network interface. Higher speed data streamed to the unit means less processing power available for decoding the resulting movie. I have had no issues with my own ripped mkvs around 10GB or less. There is not automatic firmware update notification or download unlike the WD. You need to check the A.C.Ryan website and download to a USB device then navigate the menus to start an update of the firmware. I have not updated my firmware for a couple of months so some of these observations may have changed.
Bottom line,
A.C.Ryan for the living room as the nicer menu is really a lot better for the projector than the ugly but functional WD interface.
WD live TV for the bedrooms so far, WD for the kitchen for now.
Still have another unit to buy for the 3rd bedroom and not sure which I would rather get.
I used to use my EeePC with XBMC and it was great. Took some time to get the cover art etc but it looked lovely, worked fine and I paired it with a creative remote control and IR eye. I bought some software (intelliremote or something like that) and it all worked great. Was not practical on the EeePC for a per setup and could not handle HD content due to the EeePCs processing power.
If anyone would like to know how something compares between the WD HD Live TV and the A.C. Ryan HD Mini then just ask as it is pretty easy to hook both up.
RB