He was explicit in that he was demonstrating 1:1 legacy mouse support, presumably there are other options for non-legacy games (and perhaps legacy games too?)

For example, my macbook track pad takes velocity into account. Something like that could make a big difference for covering large distances. I'm withholding judgment until I try one.

But then I play FPS with a trackball now, so it doesn't seem so alien to me.

He lifts his finger just as much in Portal play as he does in Civ. It's incredibly fast. The ergonomics of this thing make it pretty hard to say that it will be frustrating to track the cursor across the screen just because you have to lift your finger. Think about how you use a trackball. This is basically a trackpad device with the thumb ergonomics of a trackball.

The last time I touched (or saw) a trackball was a dozen years ago, so it's hard to say - but on any acceptable trackpad its dpi should allow to move across the screen in a single motion, shouldn't it?

I.e., if I move my finger across the whole steam controller right pad, then the sensitivity should be high enough to move across the whole screen in that motion while still allowing enough accuracy to click where I want.

I would be shocked if it couldn't be configured that way.

If, for example, some pad was an inch-wide and with 1000 dpi resolution, then it couldn't ever be configured to cover a 2000 pixel wide screen that way - we don't know the specs of the controller elements yet.

With some acceleration it could - finer control with small movements, but quick movements provide more travel. Not sure how well this would work, but I like Apple's implementation on their trackpad (I realise I may be in the minority here!).

It's an example of a control scheme the controller drivers allow you to come up with in order to map to a game's expected mouse-and-keyboard inputs. If a game developer wants to explicitly support the controller, then even better schemes can be designed.