To the skeptics out there: DisplayLink has had USB 2.0 video technology for years. It works great and it does 1080p just fine. I own some of thier early hardware.
Of course there are limitations. Desktop apps and web browsing work fantastic. Watching moderately and heavily compressed video looks great too (ex: YouTube). Where you hit limitations are with high graphic games and with massive video (ex: unencrypted BluRay ).