Still there is so much content you'd want to have access to on your phone: Aside from the maps, I'd love to have mobile access to tour guides, restaurant reviews, business listings, movie ratings (for next time I'm at the video rental place without a clue of what to get).
Almost every new mobile phone today comes with a memory card with ample capacity: My Nokia 6280 came with a 64 MB card. Its successor comes with 512 MB.
For the time being, this creates kind of an arbitrage opportunity for content providers: While GPRS data rates remain high, they could offer downloadable packages of offline content instead of a web service. A map of Zurich to download on the web and store on my cell phone via Blueooth? All for CHF 5? I would certainly pay for that.
This model will be viable unless data service becomes practically free: Most would probably rather pay a small flat free than put themselves at the mercy of intransparent price plans. Once data is free, it's better to use the online service as it is more up-to-date. But I doubt this will happen soon: Making data service free endangers the telcos' core business – Mobile Skype, anyone?