I have Qt Mobile Hotspot on n900 and I am able to connect to CM7 running on HP Touchpad but only when no encryption is chosen, Once I chose WEP the Touchpad Wifi is unable to connect, it says trying to obrain IP adress but never connects, once I unselect WEP it connects back, any suggestions to get around this issue.

I know WEP is not strong but atleast it will prevent anyone and everyone from using my mobile data.

the signal power out of your n900 doesnt have long range so likely someone to pick it up thats not withing few feet is unlikely. i use mobile hotspot and distance from the passanger seat to drivers seat i loose 1/3 of signal on my xoom. it may be more something with cm7 but i really wouldnt worry about others getting on it.

There is both WLAN and USB support in Mobile hotspot nowadays. Is there a plan to get also Bluetooth-PAN-support integrated?

Do not know how it would work with Windows, but for example with Linux, I would want to just run Mobile hotspot on N900, choose Bluetooth as a "Connection" method and then Start. On Linux PC pand-daemon (--listen) would notice connection established and do the deeds on that end.

It would be just so convenient consistent to have also that in Mobile hotspot and not needing to run manually separate scripts for PAN-connection in N900.

Having Bluetooth tethering is I think most suitable for me.
1) Compared to WLAN because no need to use so much power as for WLAN and broadcast packets widely.
2) Compared to USB, I can charge the battery quicker if USB is not connected to PC and were there also this feature (?) when USB is connected the CPU never sleeps.