Can I pair 2 Android Devices via Bluetooth for internet access? This is pretty much hypothetical at this point but I'm curious...
Let's say I get one of the Android tablets likely to be coming out in the spring and get one that only has WiFi and no WWAN access built in...
I've got a Moto Droid running stock 2.2.1 and unrooted.  I know I can obviously tether via wifi if I root the device, but there is also the application PDANet that allows you to tether with your computer via USB or Bluetooth.  USB is probably out of the question on most tablets, but is there any way that I would be able to tether the phone to the tablet via Bluetooth?

From what I've read, PDANet uses the DUN (Dial Up Networking) BT profile for tethering, which Android can obviously host, but is there any support in android for BT DUN client mode?

In all likelyhood I will just root (again actually... CyanogenMod almost bricked my phone) and go with that... but I'm also trying to look to the future when I will hopefully replace the Droid next summer and I don't want to become used to WiFi tethering, and then have no option upon purchasing a new phone unless I make sure that whatever I get can be rooted and run wifi-tether.
It's all possible, but it's is going to depend a lot on the particular tablet you buy.  I can tell you right now that PDANet is not going to work Android to Android.  I emailed them about this and that was their answer.  

Bluetooth tether is possible and again is going to depend on the device.  All the Archos Gen 8 tablets have BT Tethering capability (to use your phones internet) baked into the stock os, however, people are getting mixed results (by and large, this seems to be the most successful way to do it).  They had USB tether ( also to use your phones internet) but then removed it, but it is possible, it must may require some hacking.

As far as rooting and using the Wifi tether, again this is possible but people are also getting mixed results with this, myself included.  I am rooted and use Wireless Tether but my Archos 70 can't see the connection because all of the wireless tether apps create an Ad Hoc network and Android supposedly doesn't support Ad Hoc.  From what I've been told in other forums I just need to experiment with other kernels.  

If you have one of the phones with "Hotspot" capability and you pay for it through your service provider that signal is discoverable because it's an actual AP and not Ad Hoc.  

Long story short, it is possible, but there's no sure bet.  Before you buy, go to the forums for the particular tablet your interested in and read up on what it takes to get the tethering going.