Update: I've since returned to the normal Windows menu and taskbar. The dock looked nice, but was a pain to work with.
In the basic free version, you get the standard Mac-a-like system of a row of icons that magnify as you run the pointer over them. Programs that are running appear on the dock as well and when minimised, the icon turns into a little snapshot of what the screen looked like (for most programs... some fail for an unknown reason). You can also add Docklets to the dock - little programs that run on the dock itself, like the weather update script or the clock.
You lose the tray icons unfortunately, though there is a docklet that displays those icons on the dock. It's a bit unstable though, crashing the dock (and XP) quite often.
Or you can shell out for the paid version, currently in beta, which handles tray icons itself. For $20 you also get tabbed docks, which don't do the whole rolling magnification thing, but do provide for more room in the same area, and flyout menus (as seen in the screenshot) which are an icon that, when clicked, produces nested arcs of other icons through which you can scroll.
I wasn't overly keen on the tabbed docks, so the setup I've gone for is:
Across the bottom of the screen is a large dock containing the programs I use most directly on the dock, and some of the less commonly launched as themed flyout menus (games, development, yadda yadda). One thing that the free version does better than the paid is that it doesn't release the area the Windows task bar normally occupies even when the taskbar is hidden, so it was possible to have the dock displayed all the time (which would seem to be the point given the docklets). With the paid version, the windows drop underneath the dock, which means it obscures the often important status bar. So, until that's fixed, the big dock is set to autohide.
Since the dock is hidden, there's no point displaying the row of running programs on it. Instead I've put them in a second dock of small size in the top left corner of the screen. This means I'm more likely to see when they blink because they're after something... I lost track of how many messages in Trillian I missed before I did this.
It'd be nice to have the tray icons displayed there too... but you can't have a dock display both tray and running icons. So I have a third dock in the bottom right which shows those.
All-in-all, despite the little foibles, it's an effective system. I haven't tried it with games yet - non-standard UI's like these tend to have problems, but I saw that there was a program on StarDock's site which could shut down the dock if a fullscreen game was launched.