The div is gone, its now using a span - along with removing the inlineblock CSS stuff for IE.
The wrapper has no fixed height anymore, it now adapts to the input.
The left/right arrow behaviour is in the ARIA spec (or something), but Scott is talking with them (or someone, whatever) to fix that, as it makes manual keyboard entry needlessly hard.
The mousewheel intent stuff is nice, that would probably be a great addition to the mousewheel plugin. I'll ping Brandon about that.
So far only a proof of concept, but the model could work for dates, too.
Handling of invalid values is currently rather bad - enter something that can't be parsed, and it'll get dropped on blur. If you enter an invalid value, then spin, it'll reset to the default value (eg. 0), then spin. Need to do more research here, ideas and suggestions are welcome, of course.