This is a fairly new bit of kit and there don't seem to be many reviews around yet, so this might be helpful.

Design & Build
Out of the box the unit is very light. The white outer case is made of plastic but it feels pretty sturdy. Powered up there are 4 large green/yellow LCDs and a large blue power LCD, so you're probably not going to want it sitting near your TV; mine sits under my desk anyway. There is a vent underneath so putting it on carpet wouldn't be a good idea as there isn't much clearance.

Installation
Putting it together was very easy - slide the top off, 4 screws (supplied) hold the disk in place, slide the top back on and secure it with 2 screws. There's a Synology Assistant package to install on your PC that guides you through the initial setup. I'm using Windows but there are Mac and Linux versions on the CD too. You're asked if you want to use a fixed IP address of DHCP, and it guides you through installing the firmware and formatting the disk.

Performance
The disk I'm using is a 1.5TB Samsung EcoGreen F2 SATA-2 HD154UI. It runs at 5400 rpm as I was more interested in low power, temperature and noise than lightning fast access times. Copying to and from my PC using a direct connection, i.e. bypassing any switches or routers, and I was getting read and write speeds of around 25MB/s, a lot slower than the 75/38 quoted on their website. My PC and the DS110j are the only two bits of 1Gbps kit I own, so I can't tell whether it's my PC's network card or the NAS that was holding it back.

The web interface is quick to load and very responsive. The only streaming I've done so far is 720p .mkv files, and it copes with that without breaking a sweat.

Interface
I won't go into too much detail as there's a demo on the Synology website, but everything you'd expect is there. The only annoyance I've found so far is that the media server only indexes fixed folders that are auto-generated, and they don't match my directory structure. There is a way to mount them so they are visible to the media server, but for the moment I'm just streaming using network shares.

Temperature & Noise
Completely silent in standby (obviously) and quieter than a laptop when the fan is running. The SMART monitor shows the disk temperature as 27C, plenty cool enough.

I'll be using the DS110j for streaming video and music to my Asus O!Play and for storing photos. For what I'm using it for, I don't think there's anything to justify the extra cost of the QNAP TS-110 over the Synology DS110l. If I was going to be doing hardcore torrenting or running a busy website off it then the QNAP may have been a better choice for the extra RAM, but for a simple storage and streaming device the DS110j is more than adequate.