I've been asked how to do this a few times, so here is a guide:

(These instructions are based on Windows Mobile v5.0 on my Dell Axim X51V PDA. Your device may differ slightly.)

1) Select 'Settings' from the bottom of the Start Menu on the PDA.
2) Click on the 'Connections' tab at the bottom of the screen.
3) Select the Bluetooth icon.
4) On the 'Mode' tab, tick both the boxes 'Turn on Bluetooth', and 'Make this device discoverable to other devices'.
5) Turn on your DistoX, then on the 'Devices' tab, click on 'New Partnership'. The screen will show 'Scanning for Bluetooth Devices', and then list all the devices that are in range. If you get lots of devices showing up and are not sure which is your DistoX (I found 7 devices in the office at work!), then repeat this step outside away from buildings, so only your DistoX is within range.
6) Select the DistoX from the list of discovered devices (it may not appear with a meaningful name, so select the only device in the list if you get just the one item). If it was not found, click 'Refresh' to try again. Make sure the DistoX is turned on at the same time.
7) After selecting the device in the list, click 'Next' at the bottom of the screen.
8) You will be prompted for the pass-code to create the connection. Enter '0000' (four zeroes) and click 'Next'.
9) The partnership settings screen should be displayed. You can edit the display name for the device here. I suggest you give it a name to identify the specific DistoX you are connecting with here, unless you only ever plan to use one DistoX with the PDA. e.g. A name like 'Bobs DistoX'. Also in the services box below, tick the 'Serial Port' box. Then click 'Finish'.
10) You should now see the DistoX listed in the Devices list. Next click on the 'COM Ports' tab at the bottom of the screen.
11) Here we associate the DistoX with a COM port. My PDA only allows two ports to be assigned, so if you have more than two devices already set you may need to delete one of them before continuing.
12) Select 'New Outgoing Port'. On the next screen, select the device (your DistoX showing with the Display name you set previously). Then click 'Next'.
13) Select an unused COM port number from the list. (I have a Bluetooth GPS device already associated with COM8, so the only free port on my PDA was COM7. You can choose any port if you have no other devices already using them.). Then click 'Finish'.
14) You should now see you devices listed with the COM port it is using. Remember what COM port number you used, as we need to set this in the PocketTopo application.
15) Click 'OK' in the top right corner of the screen to close the Bluetooth settings screen. Your PDA will now remember the settings so you should not need to repeat this set-up stage again.

16) Start the PocketTopo application. In the menu, select Options/Port and click the same port number as you set up the device with.
17) Next tick Bluetooth/Auto on the menu (if you want the DistoX to automatically connect when in range of the PDA). Or click Bluetooth/Connect to make a connection manually.
18) You should see the blue Bluetooth light flashing on the PDA now. Wait a few seconds and the bluetooth symbol on the DistoX display should start flashing also. The PocketTopo software should then start to download any readings from the memory on the DistoX. You can see the number of readings in memory count down on the DistoX display.

Troubleshooting
---------------
My PDA has a habit of turning off Bluetooth sometimes for no apparent reason. If you do not see the blue light flashing then repeat steps 1-4 in the instructions above to turn Bluetooth back on.

I spent a happy 40 minutes surveying between trees in Chapel le Dale on Saturday evening; this included explaining to the nice policeman just what I was up to (he'd seen me from the road). He was quite interested in the end! One thing I did notice was that when in calibration mode the PDA dropped the connection between each group of shots (the few minutes I spent reading Footleg's excellent instructions!)
It soon reconnected when told to in bluetooth settings, but does this happen only in calibration, or when surveying for real? I've tried keeping both devices on for a while and it doesn't seem to do it in 'normal' mode... I set up the connection before Footleg's connection tips above, so maybe I should re do this as I just kind of bluffed it on the first go!
I might write myself a nice neat checklist for the next time, with tick boxes for each group so I don't get lost. Talking of which, anyone know how long the DistoX is likely to run on a set of Energizer Lithium batteries?

Yes, it sometimes loses the connection when surveying as well. I think it may be to do with battery saving, when you don't do anything for aa short while. Very annoying but easily re-connected manually.

I've not noticed any problems with the connection dropping with my PDA. Sometimes the DistoX is out of range during surveying (when the instrument team get carried away while I am trying to catch up with the sketching!). Sometimes I put the PDA into standby so I don't end up with garbage drawn all over the screen while it is stuffed down my suit so I can climb over something. Sometimes the DistoX powers off itself because it does so to save power if you don't press any buttons for a while. But in all cases, the DistoX and PocketTopo start talking to each other again once they are both back on and in range of each other. It does take a little while for them to notice each other sometimes, but I don't have to do anything other than wait for them to reconnect to each other.

I only see the Bluetooth turn off on the PDA when I have rebooted it, but once I turn it back on it talks to the DistoX again fine. So maybe this is something that happens on some models of PDA but not others?

Has anyone yet had any problems with the DistoX itself? We have one which is playing up and I am wondering if the board has developed a fault.

I would be interested as well as Beat has just agreed to have a look at mine after a chip seems to have gone down. This resulted in the clino either jamming on a fixed inclination or reading above +-90 degrees or working propery. The Bearing also had several possible options but these are harder to discribe but involved the reading suddenly jumping.
Beat thinks it might be the 3 way accelerometer breaking internally. This could happen if it was dropped or banged hard.
Maybe a poor batch of chips or slightly different spec from the first batch?

As to the bluetooth connections, no trouble at all, so that part and the distance section worked perfectly.

Has someone written a nice article to help explain how to take the pockettopo information and get a survey out of Therion etc?