I use Google Maps and Navigation on my Xperia Arc, and I've found it works well enough within Belgium (way more up to date than my dad's built-in satnav) and if you pre-cache the area abroad you're going to, it should help reduce data roaming charges. That said, outside or in the car, my phone locks on blazingly fast (as in, under a second), which is faster than any GPS or phone I've ever seen.