I am having a similar problem with my N800 and my iGo stowaway keyboard. It pairs up initially, and the BT icon on the N800 is 'blue'. If my N800 goes into screen-darkening standby, the BT connection is dropped. If I try to reconnect, it fails. I even tried following the exact procedure given by WoodyS in message 2 of this thread, and the pairing always fails.

Seemingly, the only way the iGo and N800 play well together is if I:

1. open an xterm window.
2. `sudo gainroot`
3. `rm -Rf /var/lib/bluetooth/<my nokia's mac address>/`
4. turn the N800 off.
5. turn the N800 on.
6. activate bluetooth and set up a new BT device
7. BT "discover" and pair with the iGo keyboard as a trusted device

...and then, everything works fine, until it stops working (which is usually when the N800 has gone to 'sleep'), at which point it's a simple matter of just starting at step 1 above and doing it all over again.

It's really quite convenient!! NOT