I've been looking at a couple Web Desktops/OS's such as EyeOS, BrowserOS(from iCUBE), YouOS, Desktop Two, and so on. This is going to be a series of round ups so look for more on this subject in the future.
EyeOS is good if you have a copy downloaded to a home machine and are running it with Apache and PHP, with the Office dependencies it requires to handle office applications. And your connection to your home machine has restricted access to only a set number of domains and is access over an https connection. So I'd vote no unless your willing to do all the work it takes to set that up. There is a demo you can if you want to try before signing up for free.
BrowserOS looks good, but it lacks applications at the moment. What I'd like to see in it would be a console similar to BASH or dos. Call me old fashioned for wanting that, but most of my best works come from the command line. This is for the Office outside of the office.
YouOS: While YouOS has a console, the interface is somewhat awkward, as though the devs wanted to have a tie in between a Mac and Windows 95. There is a slew of Apps being developed for YouOS, but you'd have to sit and sort through hundreds of apps to find the ones you want. There isn't much in terms of Office documents aside from a rich text editor. But the login interface is in https, so there is more security in keeping your password from being snagged. This has some great potential for improvement and I can't wait to see what they can pull out this year.
DesktopTwo has a petty interface but has a builtin ad-widget you cannot hide from your desktop(but on the bright-side it does stay at the bottom now). It has an office suite, MP3 player, blog, webpage, email(w/pop), IM software(use Meebo instead), message boards, etc. It's currently in the beta phase of development so you can't expect much. for now. I'd advise against it for now until the information on the site is arranged better.
Final Answer, YouOS. The interface may not be the prettiest, but it'll get the job done.