I should preface this by saying that I've never been one to learn a song unless it's something that I'm going to play in a band. I could name you my ten favorite bassists, but I've never actually sat and learned their bass lines. I'm more into the whole package (their band, tone, attitude, etc.) than I am the actual notes. Still, I'm a pretty decent player who knows plenty of songs and has never hurt for a gig. That being said.... Every few months I'll hear a flash part and think "Wow! I've got to learn that!" For example (and this one comes up for me yearly), that unison lick at the beginning of Rush's "Spirit of Radio" caught my ear and blew me away. I've tried to learn this one several times in the past to no avail. Even slowed down it escapes me. I don't lose a lot of sleep over this, as not being able to play that bit is hardly going to crush me as a musician...still, I'd be pretty impressed with myself if I nailed it.