A few things to glean from the homescreen. The official Twitter is now built in, much like Facebook was starting with 2.0. (Goodbye, third-party Twitter app market.) The singular apps button is replaced by a slightly wider widget that permanently places the dialler and browser at your fingertips - a minor tweak, but a great one, since they're two functions you want at your fingertips at all times and most Android phones don't have a dedicated phone button anymore (a phone that's easy to call with, crazy). Also, not pictured, there's a new tutorial when you bootup the phone for the first time, with lots of tips from a cute little Android.
A new automatic restore feature and an application data backup API.
Oh yes, that's right - from a software standpoint, now any Android phone can tether and be a portable Wi-Fi hotspot right out of the box. (Of course, it depends on the hardware and software too.)
Search gets a minor makeover: a blue Google button, and any easier way to narrow down precisely where you want to search - (web, contacts, apps, everything) - which developers can plug into.
A real task and application manger, neatly organised, so you can find and quickly kill any app you need to, along with the ability to move apps to and run them off of an SD card. Froyo also lets you upgrade all apps at once and adds background updating.
A new way to administer to the phone is one of a handful of new enterprise-y features, like mucho improved Exchange support.
One I missed - a better camera interface, and a zoom gesture for checking out stacks of pictures.
Besides the stuff that's visible, like the new homescreen widget and Android that greets you the first time you boot the phone, obviously a lot of the work is under the hood. It's all about speed, as you might've heard. It's hard to accurately gauge that for a couple of reasons - we've been using a pre-release build of Froyo, so things will probably get better before the final, and we didn't install any apps, at the behest of Adobe, since we were testing Flash 10.1 on this unit - but Google promises 2x-5x faster thanks to a just in time compiler. Overall, for us, the experience seemed about the same as 2.1 on the Nexus One, though there might've a bit more smoothness to transitions and animations.
We'll update with anything else we notice that's new too.