The feeling of the new windowing effect is more akin to Apple's Coverflow display instead of being reminiscent of spaces. This means no more copying text from one screen, tabbing over to another and pasting, but also no secretly running ESPN in one screen to stay tuned to the game while working on a Google Doc in the front.
Running Multiple Windows on the CR-48 In ChromeOS (Gmail and G+)
The windowing effect comes courtesy of an icon in the top right corner in what's starting to look like a menubar, with the time, WiFi signal, battery status and now a small rectangle. When running multiple windows, you can Maximize to a full screen mode, or Restore to go back to the previous status. The two foreground windows can split screen, divided in the center, which you can pull left or right to give one more or less space. Third windows and beyond get a small sliver on the right, in the order they were opened.
Writing The Blog Post In a Notepad While Checking Gmail on ChromeOS
You can still Alt-Tab between open windows, while hitting the Window button on the keyboard (for the CR-48 at least) toggles between Maximize and Restore, instead of switching windows entirely, as it had before.
The option to have multiple windows in one screen was one that I've been waiting for, since accosting Google's Don Dodge at Google IO about the feature following day two's focus on ChromeOS. For us press people, having one window to take notes and another do post those notes or do some other task is very helpful.