Hooray! My Nexus One told me this morning it had downloaded Froyo (Android 2.2) and was ready to reboot and install it when I was.
The only thing that doesn't work so far is Advanced Task Manager, which is made a bit obsolete since the OS itself how supports killing off any task. ATM would kill any task, actually, but seemed to have trouble killing itself.
The only visible change on the screen is that the app menu is now joined by an icon for the web browser to the right and an icon for making a call to the left. That's a bit redundant since I have those two icons on my center screen anyway. I suppose I can replace them with something else now.
I'm most looking forward to trying out the wifi hotspot feature that lets my phone be a wifi hotspot for any nearby devices while it's using it's 3G connection. That means that, e.g., while on a trip, everyone in the vehicle can log onto and use my phone as their wifi source for their laptops, phones, ipads, whatever. Then they can all browse the Internet, watch video, etc., at will. I've heard that you really want to have it plugged in to extra power for this, but that's not a problem in the car. Currently T-Mobile doesn't charge any extra for this.
My enthusiasm is a little lower for support for Flash on web sites. I'm sure there will be many times when I'm glad it's there. It's supposed to be pretty CPU-intensive and thus battery-draining.
A nice video about Froyo features.