I haven't played with this yet - but it looks promising for caching GMaps and other online maps to a device:
http://www.mgmaps.com/You need to take it through several steps - but for getting maps to my Blackberry it might be an interesting add on for when I'm not in tower range.
(note, I still think smartphone GPS cannot compete with dedicated GPS for 'adventuring' - but there are plenty of area here in VT and the ADKs with poor coverage)