I enjoy travelling between home and work with my iPod. Unfortunately the sound of the music plus the various noises of urban life often drown out the cellphone ring. I have the phone set to vibrate but even then I often do not register that my phone is ringing. My cellphone is a Sony Ericsson K700i with Bluetooth and touch wood it has worked perfectly with my PowerBook.
What I would love to see on the next generation iPod is Bluetooth connectivity and the option for your iPod to notify you of an incoming phone call when listening to music. OSX already notifies you of an incoming call when the phone is linked to the computer and the iPod already stores all your contacts (so presumably the bulk of the software development is already complete). It would be really nice then if Apple's synthesised voice would tell you who is calling so that I can then make the descision to answer the call or just keep listening to music.