UPDATE: Do not buy this! Sony released a firmware update recently (on 22/09/2010 I think) that disabled several 3rd party peripherals, including this adapter. It will no longer connect to the PS3 and cannot be used as input, so if you are looking for PS2 ' PS3 adapter, look elsewhere.
This is a great little adapter that does everything you could hope for. There are a few differences between the PS2 and PS3 controllers which obviously can't be overcome, such as the lack of Sixaxis motion control and proper analog triggers. However it does account for the lack of a home (PS) button by converting the analog mode button to do this function. This does not work perfectly as said button was designed as an on/off toggle so cannot recognise extended presses. Simply pressing it essentially activates the home button for a few seconds, taking you into the system menu (where you can turn the console on and off. In order to access the XMB, you have to press it, then wait a short while before pressing it again. Alternatively, pressing up+select also acts as a home button, and can be held for as long as you wish, but this can disrupt gameplay.
I previously mentioned the lack of proper analog triggers on the PS2 controller. Well, it may not have triggers as such, but all it's buttons, with the exception of start, select, analog, L3 and R3 are in fact analog, and the adapter converts this into the analog button presses of the PS3 controller, including the L2/R2 buttons. They may not be triggers, but they are pressure sensitive using this adapter, along with all the other buttons.
Unfortunately, this converter does not support vibration, which is odd as their PS2 to PC adapter does, and said adapter works on the PS3.
Also, the shape of the adapter is a little odd, in that there is a lip above the PS2 socket, which does not intrude on official PS2 controller connectors, but may on those of other manufacturers, such as the wireless dongle for Logitech's dual action controllers (which still go in, but not completely).
Overall I'd say this is a pretty good adapter. The controller number ports are a nice touch, as is the home button functionality. The only significant drawback for me is the lack of vibration.