I don't know. I spend most of my time working with NetBeans on a mac, and it's just as pretty as Keynote, while more responsive and stable. So, yeah, NetBeans, a huge Java Swing application, provides a better experience on a mac than Keynote.
>I spend most of my time working with NetBeans on a mac, and it's just as pretty as Keynote, while more responsive and stable.
Just as pretty as Keynote? I beg to differ. NetBeans (and Eclipse, IDEA) always hit the "uncanny valley" for me (and Eclipse is even using Cocoa!). Not looking right at all for the platform, and with BS divergent behaviour on lots of UI controls. On top of it, all three are quite laggy (gotten a little better with huge memory these days and SSDs, but still, if you need 4GB and solid state to get something to run fast, well...).
In no way I would say NetBeans provides a better experience on a Mac than Keynote.
That depends on the app-developer experience building GUI. Maybe most Java developers aren't that sensitive when it comes to GUI (or maybe it's a culture thing).
Having said that, not all apps have to be excellent 100% in terms of usability and beautiful-UI. Once I step out from the HN-bubble a bit I'm starting to see people using ugly but usable and solved business problems type of app written in anything from Tcl/TK, Java, Qt, Pascal, etc.
In this case the experience looks slightly different but works pretty much as expected. In other terms, the Java apps tend not to be the ones that piss me off on a regular basis.
And even for that "It runs for day's on end without being a significant burden to the rest of the system" is hardly something to write home about.