iBuyPower's Steam Machine is a decent value at $499 and the specs are not bad, however I had a few concerns with the specs presented.

http://www.theverge.com/2013/11/25/5146398/ibuypower-steam-machine-499-radeon-r9-270

The price of the config is great and will provide very good power for 1080p gaming, but I would not opt for this model for a few reasons.

1. Peak load power consumption and power supply, AMD chips are great and perform well but have much higher peak power consumption than intel cpus.  Will the power supply be sufficient when the system is under heavy load?

2. Heat disipation... unlike the Valve prototypes which have multiple independant venting systems, this unit seems to have fewer vents. given the heat of the r9-270 this may be a problem.

3. Linux based SteamOS curently has really bad driver support from AMD (hopefully this will change) but look at this review on phoronix:

http://www.phoronix.com/scan.php?page=article&item=amd_r9290_wreck&num=1

Now AMD may remedy the driver issues, and they may have a sufficient power supply and very clever heat dissipation system... but I will take a wait and see aproach on this model.  Great price if those issues are resolved.

On the other hand, the Valve prototypes are pretty sweet.

http://www.gamerheadlines.com/valve-reveals-steam-machine/

Is steam machine exclusive to NA? I think ibuypower closed down in Oz.

I'm still questioning who these machines are for because the casual consumer would rather go for a console while ardent PC gamers have other means of hooking up their PCs to a television.

I think Steam Machines will become more of a factor by 2015/16 ... when they probably have GPUs that runs circles around PS4/XB1.

I've been more than happy with both my IBP machines. Still, I don't really see the need for something like this. It will be interesting to see if the Steam Box finds a niche.