Are you missing a task switcher in GNOME Shell? Want the power-off button back? Well, you'll be glad to know that GNOME Shell supports extensions and a pack has already been released, covering these as well as some other features that you may want in GNOME Shell.
GNOME Shell Extensions is a collections of extensions providing additional functionality for GNOME Shell. The first public release was made two days ago but the extensions didn't really work because of a bug in GNOME Shell - which was fixed today.
GNOME Shell Extensions
Alternative tab: use the classic ALT + Tab
Alternative Status Menu: adds a "Power off" menu item visible at all time (and not just when pressing the ALT key) in the status menu.
Dock: shows a dock-style task switcher to the right side of the screen and is visible all the time (unlike the Dash "dock" displayed on the left that's only displayed in the "Activities" view). Right now, the dock looks almost the same as the Dash dock except it's smaller.
Gnome Shell Dock Extension comes with very basic functionality: display a list of running applications and add/remove applications as favourites:
Auto Move Windows: you can assign a specific workspace to each application.
Gajim: Integration with Gajim, a Jabber/XMPP instant messaging client.
User Theme: Loads a shell theme from ~/.themes/THEME_NAME/gnome-shell.
Windows Navigator: Allow keyboard selection of windows and workspaces in overlay mode: when you hold the ALT key, a number is assigned to each window (displayed in the top left corner) and you can then press the number to switch to that window:
Xrandr Indicator: Replace the GTK+ based indicator from gnome-settings-daemon with a native one. Lets the user rotate the laptop monitor and open display preferences quickly.
I couldn't test all the extensions because it seems not all work in Jhbuild (built in Ubuntu 10.10). But you can watch a quick video with the Dock, Windows Navigator, Power-Off back in the status menu and Alternative Tab GNOME Shell extensions below:
Apologies for the video quality (I had to stop sometimes so GNOME Shell doesn't crash because of a memory leak when recording; also the font is broken in the video for some reason - unfortunately I don't know how to fix that).
You can get the extensions @ http://git.gnome.org/browse/gnome-shell-extensions/