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]

[0] http://open.mapquest.com/ [1] Well, check the terms at http://developer.mapquest.com/web/products/open/map

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.

OpenStreetMap includes satellite view imagery from Microsoft.

osm is allowed to use Bing imagery as background reference when editing. The aireal imagery is not part of osm in any way!