I would love one of these Chromebooks. I do a fair amount of computer support by day and the potential to make life so much easier is obvious to me with Chromebooks. I bought a netbook a couple years ago looking to do just what a Chromebook does - quickly get on the web, look at some photos from our cameras on vacation, and entertain myself on the airplane. Instead, I got MS Windows which takes away any notion of doing anything quickly and adds a support load, a tiny screen which Windows clearly wasn't designed for, and 2 hour battery life. I wish the screen were just a bit bigger, the battery life alot better, and the web a bit faster.
Chromebooks hold a similar appeal to me that iPads do for many: Simplified, portable computing. They add the benefit (to me) of a keyboard so I can get something useful done, a much wider app selection I already use (the web), some useful ports for plugging in external memory and outputting to screens without buying expensive accessories, and remove Apple as my net nanny. There's no waiting for Windows Update only to launch my browser to find that there's a browser update only to finish installing that to find that there's an update to Flash that needs installing. There's not startup programs slowing my down. There's no worries about backup, whether it really went to sleep when I closed the lid, viruses, or other malware (do I trust this download?). You just open the lid, login, and you're on-line. With all that, they're still cheaper than iPads.
I'm not sure how big a deal the 3G connection is. I really like that they've bundled the connection in and removed the need for a contract. I'm doubting I'll like the pay-as-you-go rates, though, whenever they're announced. The fact that I'm already paying $30/month for an unlimited data connection from my phone and I can't use it for the Chromebook without paying even more would grate on me no matter what. I really like that they've included dual-band WiFi, though, so I can use it with my 5GHz home network.
What I'd love to see next is simpler ways to install the servers and webapp hosts at home so I could have my own private cloud. I'd rather have my photos and other files there than on someone else's service. That wouldn't stop me from getting a Chromebook, it's just what I'd like to see next. Perhaps I'll just have to start writing my own.