I own one
A few points.
Ubuntu 8.10 installed nicely. 8.04 didn't.
I had luck with both VGA out and a DVI-HDMI cable.
Wireless required ndiswrapper. Nothing complicated. Others may have more luck, but once I had it running, I was happy.
It can play 720p happily - though at high cpu usage. 1080 is a no go.
For sound I needed to use ALSA.
The computer comes with a wired keyboard, wired mouse and VESA mounting bracket. I use a gyroscopic mouse for easy control across the room.
The computer is about 70% the size of a mac mini.
One problem is a lack of USB ports. 2 on the back and 2 on the front. Keyboard and mouse can use up the back two so without using an adapter, anything else like a hard drive, bluetooth adapter etc will be stuck in the front which is unsightly.
The case is a pain to open - about as easy as opening an ipod. Once you do though, it's simple to add another 1GB sodimm to take the box to 2GB, the limit of the Atom chipset.