I usually plan my mountain-bike routes with a combination of Google Satellite and OSM. On the go, I only use the OSM, as it contains actual path data, but I haven't yet found an alternative to Google's Satellite View. There used to be tools which would scrape an area for you and use them offline, but they haven't been updated and I don't have the time do it myself.
If you want both OpenStreetMap and satellite imagery, check out MapQuest Open[0]. They provide OSM tiles and satellite imagery for anyone to use for free.[1]
I've done a lot of mapping of local mountain bike trails, followed up by making official PDFs of the trails for many local land managers. OSM is a great, great, great way to go with this, but you're right... Lacking the aerial imagery that Google provides makes things more complicated.
EDIT: That said, I have great luck with using something like OSMAnd+ to have offline sets of data that I'd contributed to. It works very nicely for electronic mapping of MTB trails.
