Since I've used smartphones with software keyboards I find myself in the habit of replying only when I get home, the phone becoming little more than a notification device.
At least on the iPad I respond a little.
I find myself seriously considering a blackberry again. I'd miss the software but know my response rate whilst mobile would soar.
The input thing is why I'm bearish on tablets in general. I like not just having a physical keyboard because it's faster and feels better, but I also like that there's a portion of my hardware that's dedicated to input. On an abstract level I feel like it is a more egalitarian paradigm, to put my ideas on the same starting level as everyone else's. It's like having upstream and downstream parity. Maybe that's silly, but it's how I feel.
That is, one dock connection that supplies power, feeds an HDMI display and connects a keyboard, transforming the ipad screen into a sort of oversized trackpad. optionally with some context sensitive controls.
With that, when people want a more traditional computing experience, they just carry their device over to the desk, dock and get on with it.
The only real missing part is OS-wide awareness of such a dock, so that the UI can shift to being more keyboard-friendly [1]. I believe even the existing dock API could effect this on a smaller scale [2] if Apple greenlit a third party to build one.
[1] Using a bluetooth keyboard with the iPad is pretty weak, due to the lack of consistent navigation support. e.g. alt-tab/cmd-tab sorts of behaviors, arrowing through pick-lists, universal tab/shift-tab support, etc.
[2] Each app would have to look for said dock (and not just on startup) and the OS still wouldn't be integrated, which would limit things a bit.
I don't think making the iPad a trackpad for an external display would work well, however, since the iPad does not have a cursor and the GUI is not designed to be used with one (try the iPhone/iPad simulator on a Mac to see how it works). Making it work as a 1-1 mapping from the iPad to the external display is what the current HDMI connector gives you anyway.
The thrust of my wonder about a possible docking solution was towards a real, actually good, option.