Youll still pay upwards of £300 for a GPS based speed camera detector a la Road Angel etc - the iPAQ does this, plus the whole SatNav thing, and most of the stuff your PC will do into the bargain - email, play MP3s and video, browse the web etc.
Its also portable unlike built in SatNav systems that you can specify on most cars now - so I can take it with me to my next motor instead of the person I sell mine to getting the benefit of the £800 odd that it costs to get a SatNav system from the manufacturer. And going from my experience of manufacturer SatNav, the TomTom stuff is streets ahead