Sometimes, when I read a Spider-Man comic book, I notice that Spidey's Spider-Sense completely fails for no good reason. For example, in ASM #24, Spidey gets taken in by Mysterio posing as a psychoanalyst and nearly reveals his secret identity to him, without his Spider-Sense warning him. That was either Stan Lee's or Steve Ditko's goof.
IMHO, Gerry Conway was particularly bad at it, with his "Spider-Man's Spider-Sense protects him only from his enemies, not his friends" idea that enabled Aunt May to break a vase over Spidey's head (ASM #114) and Professor Warren's Jackal to slash him repeatedly, without warning (ASM #148-49). (Ironically, even though Professor Warren was enough of a "friend" to Peter, notwithstanding his homicidal vendetta against him, not to set off his Spider-Sense in ASM #148, Mary Jane Watson, notwithstanding that she and Peter apparently slept together between ASM #149 and 150, apparently wasn't enough of a "friend" not to set it off at the end of ASM #149 (as Peter's Spider-Sense told him she was in his apartment).) Conway also had Spidey using his Spider-Sense like sonar (to detect the layout of Hammerhead's hideout in ASM #114) and like enhanced hearing (to hear someone on the other end of the telephone line speaking to Hammerhead, also in ASM #114).
I know a lot of people complain about the ambiguity of the spider sense, and the different ways it's portrayed by different writers. Honest to God, though, I like it. I really do. I like the ambiguity and all the different takes, it's kinda fun. I like that sometimes it only tells Peter that something bad is going to happen, whilst other times it tells him exactly where the danger is coming from, and yet others it just goes off when bad people walk past him. I like when it's used to detect radio frequencies (as is the case when Peter uses spider tracers), and when it's used as sonar (like when Peter is temporarily blinded). All that stuff is just cool to me.
That being said, that stuff about the sense only going off when Peter's enemies attacked him always seemed rather iffy to me. Never was too crazy about it. Same with the superhearing thing. That was just weird.