I purchased the Xperia Play Dock directly from Amazon - A great price and a fantastic desktop accessory for the Xperia Play.
I love my Xperia Play, and the dock, officially offered from Sony Erricson works very well indeed.
The phone is docked sideways, and the display on the phone immediately changes to display Digital Clock, Day and Date, Weather graphic with local temperature, battery charging status with current % of battery charge, and bottom menu bar - consisting on four options, alarms, media, music and android home menu.
Notification bar remains at the top and depending on your notifications will depend on what will be displayed when top menu is pulled down, such as text messaging, calls, app status etc.
The dock comes with a standard USB type cable and 13Amp plug. You can either plug the dock into your PC or into a 13Amp socket.
The display can and will time out (depending on settings) and displays a dimmed digital clock, which changes position every 20 - 30 seconds as a normal screen saver would.
You can access menus very well on the phone, when wanting to listen to some music, simply touch the music menu, which brings up a nice sideways music player press play and let the stero speakers on the phone do their thing (no speakers on the dock!)
One of the fantastic features i use a lot, is the picture slideshow. I select media - pictures and then slideshow - The phone then acts like a digital photo frame and scrolls randomly (depending on settings) through your digital picture media.
It can be used as an alarm clock, simply dock by your bed, and bang time dimly scrolls on the screen until it's time to get up!
Quite simply for the money, i would say this is a vital piece of kit to compliment the Xperia Play, being docked on it's side gives massive functionality, something that my iphone 3gs could not give me.