Honestly, I think the Steambox's biggest strengths are it's biggest weaknesses. Consoles, Ipads, handhelds, ect., are popular for their no hassle mentality. You buy one, and you're good to play all of the games for the entire gen. Steambox is open ended, and allows for upgrades. How long until the core system can no longer play certain releases, and requires an upgrade. At roughly $500 at launch, and requiring future upgrades, what's the difference inbetween it, and a pc at that point. It's fighting for a niche spot by asking for PC maintenance and pricing, to play PC exclusives, in a console market, without the name brand of a Nintendo, Sony, or Microsoft.
Then there's the games. I love Half-Life, and it's various mods, but not enough to pick it over Sony, or Nintendo exclusives. Valve releases games far too slow to make it worth buying based on their exclusives alone. Third party support will no doubtfully still release their big titles on PC, consoles, and Mac as well. Not to mention I already have HL 2 on PC, and CS on my PC, and PS3. It makes it hard to buy a console for an upgraded experience I already have on two gaming machines.
So pretty much I have 0 intrest in the Steambox. As much as I've *****ed about the PS3's RAM, I think a console having universal specs is a good thing. Steam doesn't have enough powerhouse exclusives, or release them often enough. I doubt they'll steal any significant console, let alone PC games as exclusives. The only negative, IMO, from not having one is the possible loss of Steam, and it's deals, on PC.