Desktoptwo is a web-based "operating system" manifested in a desktop that you can access from anywhere. Unlike sites like Netvibes and Protopage, which serve up RSS feeds and widgets as panels, Desktoptwo mimics your PC's desktop, complete with programs like office applications (OpenOffice), chat and email clients, calendar, contacts, and even 1GB of free hard drive space. This is more of a workspace than a startpage. It's all driven by some slick Flash.
OpenOffice can open Microsoft Excel and Word documents fairly well so even if you're tied to Microsoft Office, you can still get work done. Files can be uploaded and downloaded from the "Hard Drive" program, which acts like Explorer.
If you upload a bunch of MP3s to Desktoptwo, you can play them from the interface using the MP3 Player. A nice way to keep your music handy. The player's pretty bare bones, but sounds fine.
There are some social features like a blog and a message board available if you share your desktop with others. Not sure I'd use this, it would be like sharing your PC with a bunch of people, but I imagine, like most online social things, the kids would like it.
The rest of the apps are basic and functional. Performance is excellent and I saw no delays or hiccups. I suspect more applications will be added before it gets out of beta. All in all it's a pretty slick program that I suspect will appeal to anyone switching PCs frequently.