One word: vaporware
Besides that, what M$ previews is usually not the final product. Add to that, Microsoft's knack for pissing off its partners and customers, by making their new products obsolete. Overnight. Think wp7, kin, zune, etc...
I will never buy a mobile device with a Microsoft logo, especially with that idiot Ballmer running the show. He was an idiot in college with Gates, rode those coattails as the assclown of the group and is a complete moron now. Should be fun watching frustrated first buyers of the Surface though.
By the way, the Samsung Galaxy S3 can function like a laptop. Monitor, keyboard and mouse all functional and acts like a laptop when set up like this.