Think of bluetooth as a cable replacement. Printer cables, phone cables, serial cables, USB cables (not power cables).
I have bluetooth on my computer, T3 and v600 cell phone and here is how I use it:
I use BT on my computer so my PDA can connect to the internet through my DSL connection. This wireless connection only extends about 10 meters, so it's not a WiFi replacement.
I take MP3s on my computer and cut them down to ring-tone sizes. I then put them on an SD card and use my PDA to send the tones to my phone. Instant free MP3 ringtones, and I get to make them out of songs I like, and not some crappy rap song.
I take pictures on my phone and then send the pictures via BT to my PDA for storage. Since my phone has 5mb of memory and my PDA has 64mb plus a bigger screen, saving them on my PDA is better.
And finally, I like to keep a small amount of contacts of people I know on my phone, but in my PDA, I usually keep the numbers of places like restaraunts, stores, malls, etc. I do this so I don't have th scrool through 200 names on my phone. With BT, I can search for a contact on my PDA, hit "Dial" and it will dial the number on my phone. All I have to do is put it to my ear and it will connect for me.
Once I get a BT headset, I won't have to touch my phone at all. I can keep it clipped to my belt and wear the BT headset. I can then make my PDA dial a number, which will connect to my phone and call, and then my phone will connect to the headset. No touching the phone at all.