Ignoring the nay-sayers, there are two distinct camps when it comes to using sat nav on a bike:
1/ The 'get me from where I am to where I want to be' group who are willing to let the GPS dictate that route with some basic routing criteria such as fastest route.
2/ The power users who like to plan rides or complete continental tours, in intricate detail on their PCs and then transfer these to the GPS before heading off.
Of course there are situations where at least folk in group 2 would use the direct method and, maybe less likely, the reverse.
Most phone navigation apps would satisfy group 1. There are very few that have a sufficient range of features that would work for group 2.
One of those that would, IMHO, is CoPilot (
Android,
iPhone or
Windows). I've been testing this recently and I must say it's pretty good. Aside from not being glove friendly it covers all the requirements that, say, a Zumo 660 covers. Given a decent case for your phone such as those offered by
Ultimate AddOns it would work very well. Some form of USB power would also be a requirement. Some of the CoPilot features are, dare I say it, better than the Garmin; in app route planning, extensive configure-ability, mapping stored on phone or SD card and reasonable in file size (western Europe is about 2GB) etc. There are a few issues around resuming routes that have user defined way-points in the same vein that TomTom does, insisting that you visit any missed points before continuing. However, if you're starting out and already have a smartphone it'll cost around £100 or so for the app, case, mount and power. A darn sight cheaper than a dedicated bike at nav from Garmin or TomTom.
PC route planning can be done courtesy of ITN Converter or TYRE, the former even saves routes in the correct format.
Not going to bin my 660 any time soon but I might just get the hardware, all I really need is the case, to use this app on the bike.