TomTom is primarily a software product for road navigation. They also bundle various hardware with it. If the hardware is a normal pocket/pc PDA then there should be no reason why that PDA could not be used to run some aviation-related software, e.g. MemoryMap or Oziexplorer (the latter with self-scanned aviation charts). But I don't think TomTom software itself is any good for aviation.
Re dodgy GPS reception, nobody should use a GPS unless they have a rooftop aerial (antenna). I know the current Garmins with their integral aerials do tend to work, in an all-metal aircraft, 99% of the time... This is not an argument against GPS; it is an argument against the owner of an aircraft who is not willing to spend say £300 to get a proper GPS aerial fitted.