Since I need a modem on the road first thing I needed to setup was USB/Bluetooth tethering for my Powerbook with my N900.
I had so much trouble with blackberry/Palm Pre/other smart phone tethering in the past that I thought I'd start in the morning so I have all day to figure that one out.
Well, after 2 minutes I was done. I was rather amazed.

Step 1:
Plug-in N900 with USB cable into Mac

Step 2:
Select PC Suite mode on your N900

Step 3:
Select this:


Enter *99# for the phone number

Step 4:
Click on Advanced
Enter the APN as shown below (T-Mobile USA only)


Click Connect and voila:


Hope this helps.