I actually think this thing is a little overpriced, as are many of the "Official" PS3 accessories. But alas, it's not bad.
The keypad is a small platform that mounts right onto the PS3 controller. Please note that it does NOT feed off of the controller, and has its own battery, as well as a mini-USB port (just like the controller one) to charge it with. The PS, Start, and Select buttons aren't actually electronic, and have small nubs on the other side to push their actual corresponding buttons on the controller. This way, you can still play games perfectly fine with the keypad turned off.
The keypad does not come with a USB cord to charge with, so you'll have to use the one that should have come with your PS3 (or any others you might have). When you first flip the on switch on the right side, nothing happens. When not in use, the keypad sits in standby mode and doesn't generally use much charge. Since the on/off switch isn't especially conspicuous, and the keypad really does act like it's completely off when not in use, I can see it being quite easy to leave it on by mistake. Fortunately, the battery life is fairly generous. I don't have any estimates, but it didn't falter once throughout an intense 2-3 hour chat session in PS Home, and it hasn't yet failed to flicker to life whenever I press a button while the switch is on. It connects to the PS3 just as any controller would. You turn it on, and press a button, and it will search for and, within a few seconds, connect to the system. Just as with a controller or PS headset, you can instantly pair it via a USB cable. By the way, you can actually use this with other bluetooth devices that support wireless keyboard functionality. Be that a computer or a cell phone, I thought that was a nice piece of info.
Typing on the keypad is a mixed bag. It's not especially difficult to reach the keys, but, (unsurprisingly), its not a miracle pad that will allow you to play games while typing. Besides the regular alphabet and numbers, you use the shoulder buttons to access much of the punctuation tools, and most of the more advanced symbols. Really, it works similarly to a calculator in that respect. This takes some getting used to, but what keyboard doesn't require a bit of practice time before you're up to speed? However, unless you use this thing on a very regular basis and thus are used to the full layout of the symbols, you will find it difficult to type anything particularly eloquent with this thing. For quick jots and notes, it's quite excellent, but this is no replacement for a full sized keyboard.
The keyboard also has two shortcut keys. One takes you directly to your message inbox, and the other opens the XMB to the Friend tab. I don't actually use the inbox much (I'm more in the habit of using the "Message List" option on friends), so I didn't make much use of these shortcuts. But they were a nice thought, nonetheless.
I thought the keys were spaced decently, though I did mistype a couple characters on a mildly frequent basis.
The other major features of the keyboard is touchpad functionality. I don't have any idea how they made this work, but it does, to some extent. You just press a little button near the bottom of the pad, and that converts the entire board into a touchpad. You just run your finger over the keys to move the cursor. It's quite a bit wonky until you calibrate it, but I was just fine using the analog sticks. It's a nifty feature, but just like the touch buttons on the PS3, I think Sony went a bit overboard adding it in.
Overall, the PS Keypad is a decent pad. Yes, decent. After spending about two weeks using it, I still don't think it's worth its $40-50 price tag, but it's not a horrible device. Average, I suppose.