This isn't necessarily new--I think I saw this a while back in the PC client--but Microsoft offers a Games for Windows LIVE software download service called Games On Demand, which appears to be similar/identical to Xbox LIVE's Games on Demand. I assumed, this being the Windows version, that there'd only be a tiny number of titles compared to what's available on the console (177). But actually, it's not too shabby: There are about 80 titles available, including a few new(ish) games like BioShock 2 and Dead Rising 2. It's not exactly Steam, but then what is?
But wait, there's more: Apparently, the new bit is that Microsoft is opening up a web-based marketplace for Windows games called Games for Windows Marketplace. It's coming November 15. The Games on Demand service noted above only works through the terrible Games for Windows LIVE client software.
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ZD's Rachel King got to experience HP's upcoming Windows 7-based Slate PC, which is interesting. But she came away with the exact opposite reaction that I have (I've not seen one in person, however): "It certainly seems that HP made the right decision by going business-friendly with this one." Eh? But we can agree this bit: "This is definitely not a competitor for the iPad." Exactly so.
It's supposed to be available now, but I don't see it on HP.com. $800.