I use the Mitsumi Bluetooth Dongle and it works very well. Wondows 200 Pro, I don't know about any other operating system. I had similar issues as those mentioned and was ready to throw it in the dustbin when I finally came accross some advice on another message board. The following instructions are what I did, it now works smoothly both on my desktop and laptop pc's running windows 2K pro.
I take absolutely no credit for the following instruction, someone way more clever than I am came up with this:
1. Uninstall ANY instance of Bluetooth sw in your computer (Widcomm, Mitsumi BT Suite, Blue Manager.. watever)
2. Restart the computer (remember to unplug the mitsumi from the usb port)
3. Download the MSI Software (I haven't tried the rest yet but this one works fine for me)
http://download.msi.com.tw/support/dvr_exe/bt45.exe
4. Install the sw and restart your computer.
5. Plug in your mitsumi and go to your device manager.
6. You should see an unknown USB DEVICE.
7. Now here comes the real deal. Go to C:\Program Files\Microstar\Bluetooth Software\bin\btwusb.ini
8. Open that file with a notepad and edit the following line.
VID_0db0&PID_1967 to
VID_03EE&PID_641F
There are two instances of it. So change BOTH of them. This line is to allow windows to detect the mitsumi device that u plugged in.
9. Save and restart your computer.
10. Go to your device manager -> select the USB Device -> Reinstall driver
11. Select the microstar path that i have previously mentioned and choose btwusb.ini
12. Windows should install the necessary sw for it !!
13. Restart the comp again and go to your BT Places.
14. Do a search for devices and you should see your device.
Hope this helps