In reply to Indy:
I mostly use the base maps on Garmin Connect, but like you say, it can lead you up rough tracks if you're not careful, so I also look at Google Earth streetview where available (usually for the urban bits) and also good old OS maps.
I like planning rides, but I also dislike over-planning. To a certain extent getting temporarily lost can add to the overall fun - just depends what sort of ride you want that day.
I did JOGLE last year using the system above. Uploaded the lot to a Garmin Edge 200 - job done.
N