"I never see my desktop because it's always covered with windows. What use is plasma to me?"
"Will plasma have a MacOS Dashboard style mode where the widgets pop on top?"
i hear these two questions about plasma often enough that i'm dedicating a blog entry to answering it. first, here's my obviously biased opinion of mac os dashboard: pretty but flawed.
there are some truly nicely designed widgets for it, but here's why i think mac os dashboard falls short:
reason 0: it's heavy. i was amazed at how much ram that thing took. and for just a screen cover layer?
reason 1: it's only available as an over-the-top-of-your-windows thing leaving you, the user, in the "modal muddle". forcing people to choose between modes of operation with no flexibility is stupid.
reason 2: they beat me to implementing the full screen widget display. this is my "sour grapes" reason ;)
in my earliest design presentations on plasma, i had a slide that showed the concept of allowing the desktop to be "z ordered" above other windows. i even had a crappy little graphic showing the concept because it was otherwise hard to get across to people at first because there wasn't anything i could point to and go "see, that's what i want to do". ("hm? desktop above windows? but.. it's the desktop, right?") that is, until dashboard arrive in the spring of 2005 with tiger. damn them! ;) while i was waiting for kde4 devel to start with all my plans tucked neatly away in my pockets, they were developing something that had a number of similar features. ah, the 100th monkey syndrome strikes again!
but they didn't go far enough, imho. it's too much of a heavy-handed add-on-esque thing. it also doesn't really change much about how you use your computer; but then to be fair neither have any of the other gadget factories, really.
in any case, to answer the original questions:
yes, you will be able to flip your desktop contents to the front of your windows if you have a composition manager around. the latter is because without it i can't make the background translucent, which i think is a basic requirement for this feature (so people don't freak out that they've lost their windows). maybe i'll change my mind on that so that if you don't have a composition manager running you just get the classic "show desktop" effect? perhaps.
also remember that you will be able to put these widgets on panels or even free floating about. you will eventually also be able to go into "media center" mode and see widgets integrated there as well. huzzahs all around.
so yes, even with all your windows in the way, plasma will still be relevant to you. remember that it's replacing kicker (the panels and taskbar) too while bringing other presentation formats with it.
and this was all planned somewhere between 2 and 3 years ago (was i showing this stuff off in ludwidsberg? i can't remember now...). not to have thought of this issue would have been a pretty major oversight. to paraphrase jessica rabbit, "i'm not stupid, i'm just drawn that way."