There are many web os of the present,
you can create docs, upload docs to OS and store there, but U cant download. But there is no scope of Im and e-mail.
allows you to store 5 GB free files on a central server and 3 GB of e-mail and has inbuilt IM and E-Mail
This has two interesting features website editor and blogger.
So man web os's are evolving by the day and the advantage is portability of your work environment from any location.
So it is a virtual laptop which can be accesseed from any PC. I would say it is very impressive and in future would get even full fledged.