The steps I do to pair are:

On the PS3 go to the menu Settings > Accessory Settings > Manage Bluetooth Devices.
Press Register New Device and Start Scanning

On the n810 I make sure bluetooth is on and open bluemaemo.

The PS3 will as to enter a key which i typed into the n810.
It then gives a message that they are now connected (the n810 just says "Connected to:", as in the ps3 does not have a name)

To use the most keys (including direction buttons) you have to be on the keyboard profile or assign them in the game controller.

To use the triangle button you have to be on the mouse profile.

The buttons are:
Triangle: Right mouse button
Square: backspace
Cross: enter
Circle: Escape (back button)