Learning songs by "ear"
Well, it depends on the song. I really believe that my ear is one of my weaker areas, and there have been a couple of times were I was just listening to a song on the car radio, and when I got home, I picked up my bass, and could play it. This is largely because what I heard more was the chords, and the progression, and was able to anticipate what the bass player was doing. There are plenty of other songs that take a long long time for me to figure out, and there are certainly some others that I'm still hammering out.
Whatever happens though, don't give up. Sometimes it helps just to walk away from the piece, and have at it later. Each and every single song you do, it will get easier. I guarantee it.