I do use earbuds with my mp3 when I'm riding the railtrail and I'm by myself. I do not keep it loud, simply loud enough to hear. I do have a habit of riding and singing when nobody else is around to hear. The singing does tend to flush the critters out of my way before I'm close enough to startle them! (I do the same when I'm riding horse - sing out loud ... yes, I'm a freak).

I have a mirror and am very aware of who's behind and ahead of me, which is rarely anyone. There's rarely bike traffic, so I rarely encounter people who are traveling in the same direction as me, if I do, I'm generally the one passing. I don't fiddle with buttons - whatever plays plays.

I will only use the mp3 on very low-traffic rail trails and never on streets or when in a group (well, with hubby - that's as big of group as I ever get). When a cyclist does approach me from behind, even though I have my mirror, I always acknowledge to them that they are seen so they can know I heard/saw them and can pass with confidence. I don't feel I'm any more dangerous with them than without them - although I know some will disagree.