The Google Chrome OS

I donno. Lots of people seem to like it.

I actually do have a personal email server, but that's besides the point.

One possible reason:

Normally if I wanted to setup a secure network then I would be very very careful about what sort of things I allow on it. Preferably no network access at all. Once your inside the network it's trivial to circumvent any sort of network security by using various tunnelling protocols. I've tunnelled through restrictive http proxies using openvpn. Tunnelled out of networks over DNS, and other happy stuff of that sort.

If I have users that depend on email, but need to operate in a secure intranet-only network, then it would make sense to setup webmail on a server on the 'secure' network and make people use that for checking up on things. Then that server would have a separate network access to a external network. I would definitely not want to allow even https over a proxy to contact Gmail, but Gmail is a familiar interface for people so maybe I'd want to provide that on the server.

That's just one possibility.

Otherwise there are nice search features and anti-spam stuff that Google does that are very proprietary that many people would probably want to learn from.

*shrug*