It doesn't work with QWidget based popups yet, though there's no reason it couldn't; Plasma::Dialog just doesn't have the logic for it yet. That means that things like kickoff or the device notifier still behave a bit magically.
I'm pretty sure that when we do extend it to all "things that come out of an edge docked panel" that we'll need to make it configurable (though it turns off automatically when animations are cut in plasma as a whole or when there is no compositer around) since some people will likely absolutely hate it for reasons of personal taste. I think it's jolly good (to use a quaint Britishism), but I can just tell it's the sort of thing someone, somewhere will take umbrage with.
It also occurs to me that this would be so much better as a compositing plugin. However, at least to my knowledge (and please correct me if I'm wrong, window manager people), there's very little interaction possibility between individual windows and the compositing effects. While usually this is perfect (you don't want random windows doing random things because their app developers feel they really ought to have spinning-breaking-apart-windows), in this case it makes me put code in a place it really doesn't belong (the application).
It would be terrific if a window could say "Ok, now slide me out into that other window over there on these positions." We actually already do this for the minimize effects by publishing the location that a window should minimize to/from. I actually tried using that but the results weren't exactly what I wanted because it meant positioning, minimizing then restoring the window and even then it didn't exactly work right (perhaps because the window is set to skip taskbar?).
There are a few such things that would be just awesome to be able to do with more comprehensive application<->window manager interaction possibilities. Which led me to think what now seems like the bleedingly obvious:
It would be beyond awesome to have a window manager developer sprint that focuses on application <-> window manager interaction issues
Such a thing would be attended by people writing high-energy window managers (KWin and Compiz would be two "must haves" there IMHO .. who else? E17, XFCE, Metacity?) and people writing applications or frameworks that could take advantage of such things (e.g. Plasma for the obvious reasons; Qt and KDE lib for thing like document modal dialog (aka "sheets" on MacOS) .. there must be others out there too :).
The goal should be to walk away with a set of agreed upon capabilities, interaction patterns, trigger mechanisms and even some initial implementations in the apps and window managers. It would be great to see things like the "slide 'n hide" window effect we now have in Plasma, sheets, the ability to ask for specific groups of windows to be shown in the currently active window switching style (e.g. present windows or cover flow or whatever the user has selected) for use by things like grouping task bars ... so many possibilities.
I really don't have time for such a thing before the summer is out, but maybe I'll try and hook something up after then. Or maybe one of you could hook it up. The world neither revolves nor depends on me, after all. :)
p.s. Apologies for the lack of screencasts lately, a lot of the stuff I have going on looks best with compositing and my compositing screencasting set up is in pieces atm.
p.p.s. Rob's been doing some rather nice work on improving the feedback when jobs and notifications are hosted in the systemtray; can't wait for that to settle in and for him to screencast that stuff. :)