If I hear something I want to learn, like off the radio (and it doesn't happen very often, with the radio), I will try to catch the title and artist, then when I'm at the computer, I'll google the tablature. I uaually won't get actual tablature, but I'll end up with lyrics and chords. Then, I'll try to play it on the guitar and see if I can make it come out like I remember.

If--and this happens more often--I catch the song in somebody's live performance, I will watch real careful what the rhythm guitarist is doing, listen real careful to what the bass player is doing (because I can usually follow bass lines), and afterwards catch one of the band (or the artist, if there's only one of him/her) and ask who wrote it and what the name of the song is. And then do the google-tablature and try-to-play-it things.

Doesn't happen often, because there are very few songs written by anybody else that I can sing because my voice range is too narrow. Of the two that I did pick up during the past couple of years, one was a Doc Watson tune I heard on the radio (good for him!) and the other was a Tom T. Hall song I saw performed by a bluegrass band.

Mostly, I don't worry about it much, because I'm not going to be performing cover songs in public anyway. When I play live, it's almost always exclusively my stuff, anyway (and most of the groups I play with have gotten used to me and expect it), and my excuse is that I virtually can't sing anybody else's stuff.

The Artist Formerly Known as Moonless Joe