My issue with systems like this is that they consume valuable horizontal real estate. Like most people, I use a widescreen monitor. To take full advantage of this, I use a tiling window manager (Xmonad) and typically use two browser windows side-by-side, akin to a full two-page broadsheet newspaper. Putting a tab bar on the side of each window would consume nearly 1/3 of the screen and generally get in the way of the content.