Great bit of kit
I've had an EX470 which was an earlier version with a little less processing power and ram. I threw in a 1GB stick and its been fine since.
In respect of some of the other comments though, its method of drive pooling (and per share configured file duplication if you want it) is not as good as raid in some senses but this is a home server and it does allow you to use whatever drives you have spare. Another upside is each drive is readable in its own right and should your server get trashed you can plug a drive into any windows box and access the files, although this will be lost in the upcoming version of WHS which uses a new filesystem instead of NTFS. Also the OS and all configuration sits on the first drive. You can upgrade it but if you plan to do so i recommend replacing it before you start loading data onto the server.
You probably could put Linux on this but its a headless server there is no monitor connection unless you look up the hacked together cables that some people have made. Its built/rebuilt via a network enabled imaging package. This might cause you some difficulty in actually getting Linux on there or troubleshooting it if you have an issue
Pros: You can run windows services off it, I have mine configured as a shared print server, bind DNS server (because ISP dns servers are flakey), Teamspeak3 server for gaming, it also runs uTorrent and i've even put a dedicated game server or two on there at times. HP also build there hardware to be friendly to being taken apart and dont invalidate your warrantee if you want to upgrade the RAM. I bought mine as an ex-display with no drives, drivetrays, cables and no software. I had my own spare drives and cables and HP sent me out drive trays and software for free. The remote access works great if you make sure your router is forwarding the ports correctly
Its features list being able to stream your video files but this is not done via on-the-fly conversion. Instead it runs a video converter that will create streamable copies using up additional space. It does this by default for your entire video library which is downright annoying. Also the media sharing options are a bit all over the place. Itunes/Windows Media/Inbuilt uPnP media server are configured separately and the windows media network sharing service is just a horrible performance killer
Overall though, its a cut down windows server and that has advantages. Disable the stuff you dont like and enjoy the fact that your high powered gaming rig doesnt need to be online all night for the sake of some low speed downloads that you want to leave running, Not to mention offloading your storage onto one of these means you dont need masses of storage on your PC and can switch to SSD disks