If Thin ITX is not going to win in retail, it seems more and more interesting for some integrators. For example, English Tranquil PC unveiled a beautiful multimedia-oriented machine, based on Intel DH61AG.
Inside, there are the big fat configuration: i3 2100T, 4GB of RAM, a small 80GB mSATA SSD, DVD, etc.. The price, now in promotion, is £649. However, for £ 278 you can buy the barebone, ie its passive cooling system and the motherboard.
You may get more information at tranquilpcshop.co.uk.